forked from OSchip/llvm-project
[X86] avoid assert with varargs, soft float, and no-implicit-float
Fixes: - PR36507 Floating point varargs are not handled correctly with -mno-implicit-float - PR48528 __builtin_va_start assumes it can pass SSE registers when using -Xclang -msoft-float -Xclang -no-implicit-float On x86_64, floating-point parameters are normally passed in XMM registers. For va_start, we spill those to memory so va_arg can find them. There is an interaction here with -msoft-float and -no-implicit-float: When -msoft-float is in effect, instead of passing floating-point parameters in XMM registers, they are passed in general-purpose registers. When -no-implicit-float is in effect, it "disables implicit floating-point instructions" (per the LangRef). The intended effect is to not have the compiler generate floating-point code unless explicit floating-point operations are present in the source code, but what exactly counts as an explicit floating-point operation is not specified. The existing behavior of LLVM here has led to some surprises and PRs. This change modifies the behavior as follows: | soft | no-implicit | old behavior | new behavior | | no | no | spill XMM regs | spill XMM regs | | yes | no | don't spill XMM | don't spill XMM | | no | yes | don't spill XMM | spill XMM regs | | yes | yes | assert | don't spill XMM | In particular, this avoids the assert that happens when -msoft-float and -no-implicit-float are both in effect. This seems like a perfectly reasonable combination: If we don't want to rely on hardware floating-point support, we want to both avoid using float registers to pass parameters and avoid having the compiler generate floating-point code that wasn't in the original program. Instead of crashing the compiler, the new behavior is to not synthesize floating-point code in this case. This fixes PR48528. The other interesting case is when -no-implicit-float is in effect, but -msoft-float is not. In that case, any floating-point parameters that are present will be in XMM registers, and so we have to spill them to correctly handle those. This fixes PR36507. The spill is conditional on %al indicating that parameters are present in XMM registers, so no floating-point code will be executed unless the function is called with floating-point parameters. Reviewed By: rnk Differential Revision: https://reviews.llvm.org/D104001
This commit is contained in:
Bob Haarman
parent
a11880468e
commit
3bc899b4de
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@ -3377,12 +3377,8 @@ static ArrayRef<MCPhysReg> get64BitArgumentXMMs(MachineFunction &MF,
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return None;
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}
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const Function &F = MF.getFunction();
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bool NoImplicitFloatOps = F.hasFnAttribute(Attribute::NoImplicitFloat);
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bool isSoftFloat = Subtarget.useSoftFloat();
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assert(!(isSoftFloat && NoImplicitFloatOps) &&
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"SSE register cannot be used when SSE is disabled!");
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if (isSoftFloat || NoImplicitFloatOps || !Subtarget.hasSSE1())
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if (isSoftFloat || !Subtarget.hasSSE1())
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// Kernel mode asks for SSE to be disabled, so there are no XMM argument
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// registers.
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return None;
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@ -3454,11 +3450,6 @@ void VarArgsLoweringHelper::createVarArgAreaAndStoreRegisters(
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FrameInfo.CreateFixedObject(1, StackSize, true));
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}
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// Figure out if XMM registers are in use.
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assert(!(Subtarget.useSoftFloat() &&
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TheFunction.hasFnAttribute(Attribute::NoImplicitFloat)) &&
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"SSE register cannot be used when SSE is disabled!");
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// 64-bit calling conventions support varargs and register parameters, so we
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// have to do extra work to spill them in the prologue.
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if (is64Bit()) {
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@ -0,0 +1,81 @@
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; RUN: llc -mtriple=x86_64-unknown-unknown < %s | FileCheck %s
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%struct.__va_list_tag = type { i32, i32, i8*, i8* }
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declare void @llvm.va_end(i8*) #0
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declare void @llvm.va_start(i8*) #10
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define void @hardf(i8* %fmt, ...) #1 {
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; CHECK-LABEL: hardf
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; When using XMM registers to pass floating-point parameters,
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; we need to spill those for va_start.
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; CHECK: testb %al, %al
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; CHECK: movaps %xmm0, {{.*}}%rsp
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; CHECK: movaps %xmm1, {{.*}}%rsp
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; CHECK: movaps %xmm2, {{.*}}%rsp
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; CHECK: movaps %xmm3, {{.*}}%rsp
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; CHECK: movaps %xmm4, {{.*}}%rsp
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; CHECK: movaps %xmm5, {{.*}}%rsp
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; CHECK: movaps %xmm6, {{.*}}%rsp
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; CHECK: movaps %xmm7, {{.*}}%rsp
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%va = alloca [1 x %struct.__va_list_tag], align 16
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%arraydecay = getelementptr inbounds [1 x %struct.__va_list_tag], [1 x %struct.__va_list_tag]* %va, i64 0, i64 0
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%a = bitcast %struct.__va_list_tag* %arraydecay to i8*
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call void @llvm.va_start(i8* %a)
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call void @llvm.va_end(i8* nonnull %a)
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ret void
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}
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define void @softf(i8* %fmt, ...) #2 {
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; CHECK-LABEL: softf
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; For software floating point, floats are passed in general
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; purpose registers, so no need to spill XMM registers.
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; CHECK-NOT: %xmm
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; CHECK: retq
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%va = alloca [1 x %struct.__va_list_tag], align 16
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%arraydecay = getelementptr inbounds [1 x %struct.__va_list_tag], [1 x %struct.__va_list_tag]* %va, i64 0, i64 0
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%a = bitcast %struct.__va_list_tag* %arraydecay to i8*
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call void @llvm.va_start(i8* %a)
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call void @llvm.va_end(i8* nonnull %a)
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ret void
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}
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define void @noimplf(i8* %fmt, ...) #3 {
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; CHECK-LABEL: noimplf
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; Even with noimplicitfloat, when using the hardware float API, we
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; need to emit code to spill the XMM registers (PR36507).
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; CHECK: testb %al, %al
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; CHECK: movaps %xmm0, {{.*}}%rsp
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; CHECK: movaps %xmm1, {{.*}}%rsp
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; CHECK: movaps %xmm2, {{.*}}%rsp
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; CHECK: movaps %xmm3, {{.*}}%rsp
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; CHECK: movaps %xmm4, {{.*}}%rsp
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; CHECK: movaps %xmm5, {{.*}}%rsp
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; CHECK: movaps %xmm6, {{.*}}%rsp
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; CHECK: movaps %xmm7, {{.*}}%rsp
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%va = alloca [1 x %struct.__va_list_tag], align 16
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%arraydecay = getelementptr inbounds [1 x %struct.__va_list_tag], [1 x %struct.__va_list_tag]* %va, i64 0, i64 0
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%a = bitcast %struct.__va_list_tag* %arraydecay to i8*
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call void @llvm.va_start(i8* %a)
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call void @llvm.va_end(i8* nonnull %a)
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ret void
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}
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define void @noimplsoftf(i8* %fmt, ...) #4 {
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; CHECK-LABEL: noimplsoftf
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; Combining noimplicitfloat and use-soft-float should not assert (PR48528).
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; CHECK-NOT: %xmm
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; CHECK: retq
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%va = alloca [1 x %struct.__va_list_tag], align 16
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%arraydecay = getelementptr inbounds [1 x %struct.__va_list_tag], [1 x %struct.__va_list_tag]* %va, i64 0, i64 0
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%a = bitcast %struct.__va_list_tag* %arraydecay to i8*
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call void @llvm.va_start(i8* %a)
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call void @llvm.va_end(i8* nonnull %a)
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ret void
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}
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attributes #0 = { nounwind }
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attributes #1 = { nounwind uwtable }
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attributes #2 = { nounwind uwtable "use-soft-float"="true" }
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attributes #3 = { noimplicitfloat nounwind uwtable }
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attributes #4 = { noimplicitfloat nounwind uwtable "use-soft-float"="true" }
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