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Revert "[InstCombine] Fix miscompile on GEP+load to icmp fold (PR45210)" 

This reverts commit 4f2fd3818b.

The Linux kernel fails to build after this commit. See
https://reviews.llvm.org/D99481 for a reproducer.

Signed-off-by: Nathan Chancellor <nathan@kernel.org>
This commit is contained in:
Nathan Chancellor 2021-05-31 20:11:46 -07:00
parent 372237487e
commit e6b086bef2
No known key found for this signature in database
GPG Key ID: 1D6B269171C01A96
2 changed files with 12 additions and 36 deletions
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22
llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
View File

@ -269,30 +269,14 @@ InstCombinerImpl::foldCmpLoadFromIndexedGlobal(GetElementPtrInst *GEP,
// order the state machines in complexity of the generated code.
Value *Idx = GEP->getOperand(2);
// If the index is larger than the pointer size of the target, truncate the
// index down like the GEP would do implicitly. We don't have to do this for
// an inbounds GEP because the index can't be out of range.
if (!GEP->isInBounds()) {
// If the index is larger than the pointer size of the target, truncate the
// index down like the GEP would do implicitly. We don't have to do this
// for an inbounds GEP because the index can't be out of range.
Type *IntPtrTy = DL.getIntPtrType(GEP->getType());
unsigned PtrSize = IntPtrTy->getIntegerBitWidth();
if (Idx->getType()->getPrimitiveSizeInBits().getFixedSize() > PtrSize)
Idx = Builder.CreateTrunc(Idx, IntPtrTy);
unsigned ElementSize =
DL.getTypeAllocSize(Init->getType()->getArrayElementType());
// If inbounds keyword is not present, Idx * ElementSize can overflow.
// Let's assume that ElementSize is 2 and the wanted value is at offset 0.
// Then, there are two possible values for Idx to match offset 0:
// 0x00..00, 0x80..00.
// Emitting 'icmp eq Idx, 0' isn't correct in this case because the
// comparison is false if Idx was 0x80..00.
// We need to erase the highest countTrailingZeros(ElementSize) bits of Idx.
if (countTrailingZeros(ElementSize) != 0) {
Value *Mask = ConstantInt::getSigned(Idx->getType(), -1);
Mask = Builder.CreateLShr(Mask, countTrailingZeros(ElementSize));
Idx = Builder.CreateAnd(Idx, Mask);
}
}
// If the comparison is only true for one or two elements, emit direct

26
llvm/test/Transforms/InstCombine/load-cmp.ll
View File

@ -33,8 +33,7 @@ define i1 @test1(i32 %X) {
define i1 @test1_noinbounds(i32 %X) {
; CHECK-LABEL: @test1_noinbounds(
; CHECK-NEXT: [[TMP1:%.*]] = and i32 [[X:%.*]], 2147483647
; CHECK-NEXT: [[R:%.*]] = icmp eq i32 [[TMP1]], 9
; CHECK-NEXT: [[R:%.*]] = icmp eq i32 [[X:%.*]], 9
; CHECK-NEXT: ret i1 [[R]]
;
%P = getelementptr [10 x i16], [10 x i16]* @G16, i32 0, i32 %X
@ -45,8 +44,8 @@ define i1 @test1_noinbounds(i32 %X) {
define i1 @test1_noinbounds_i64(i64 %X) {
; CHECK-LABEL: @test1_noinbounds_i64(
; CHECK-NEXT: [[TMP1:%.*]] = and i64 [[X:%.*]], 2147483647
; CHECK-NEXT: [[R:%.*]] = icmp eq i64 [[TMP1]], 9
; CHECK-NEXT: [[TMP1:%.*]] = trunc i64 [[X:%.*]] to i32
; CHECK-NEXT: [[R:%.*]] = icmp eq i32 [[TMP1]], 9
; CHECK-NEXT: ret i1 [[R]]
;
%P = getelementptr [10 x i16], [10 x i16]* @G16, i64 0, i64 %X
@ -55,14 +54,10 @@ define i1 @test1_noinbounds_i64(i64 %X) {
ret i1 %R
}
; When x is 0x8009, x * 2(ElementSize) overflows and it becomes 0x0012.
; It is the same location as when x is 0x0009, So we need to return
; true if x AND 0x7FFF is 0x0009.
define i1 @test1_noinbounds_as1(i32 %x) {
; CHECK-LABEL: @test1_noinbounds_as1(
; CHECK-NEXT: [[TMP1:%.*]] = and i32 [[X:%.*]], 32767
; CHECK-NEXT: [[R:%.*]] = icmp eq i32 [[TMP1]], 9
; CHECK-NEXT: [[TMP1:%.*]] = trunc i32 [[X:%.*]] to i16
; CHECK-NEXT: [[R:%.*]] = icmp eq i16 [[TMP1]], 9
; CHECK-NEXT: ret i1 [[R]]
;
%p = getelementptr [10 x i16], [10 x i16] addrspace(1)* @G16_as1, i16 0, i32 %x
@ -265,8 +260,7 @@ define i1 @test10_struct_arr(i32 %x) {
define i1 @test10_struct_arr_noinbounds(i32 %x) {
; CHECK-LABEL: @test10_struct_arr_noinbounds(
; CHECK-NEXT: [[TMP1:%.*]] = and i32 [[X:%.*]], 268435455
; CHECK-NEXT: [[R:%.*]] = icmp ne i32 [[TMP1]], 1
; CHECK-NEXT: [[R:%.*]] = icmp ne i32 [[X:%.*]], 1
; CHECK-NEXT: ret i1 [[R]]
;
%p = getelementptr [4 x %Foo], [4 x %Foo]* @GStructArr, i32 0, i32 %x, i32 2
@ -300,9 +294,7 @@ define i1 @test10_struct_arr_i64(i64 %x) {
define i1 @test10_struct_arr_noinbounds_i16(i16 %x) {
; CHECK-LABEL: @test10_struct_arr_noinbounds_i16(
; CHECK-NEXT: [[TMP1:%.*]] = sext i16 [[X:%.*]] to i32
; CHECK-NEXT: [[TMP2:%.*]] = and i32 [[TMP1]], 268435455
; CHECK-NEXT: [[R:%.*]] = icmp ne i32 [[TMP2]], 1
; CHECK-NEXT: [[R:%.*]] = icmp ne i16 [[X:%.*]], 1
; CHECK-NEXT: ret i1 [[R]]
;
%p = getelementptr [4 x %Foo], [4 x %Foo]* @GStructArr, i32 0, i16 %x, i32 2
@ -313,8 +305,8 @@ define i1 @test10_struct_arr_noinbounds_i16(i16 %x) {
define i1 @test10_struct_arr_noinbounds_i64(i64 %x) {
; CHECK-LABEL: @test10_struct_arr_noinbounds_i64(
; CHECK-NEXT: [[TMP1:%.*]] = and i64 [[X:%.*]], 268435455
; CHECK-NEXT: [[R:%.*]] = icmp ne i64 [[TMP1]], 1
; CHECK-NEXT: [[TMP1:%.*]] = trunc i64 [[X:%.*]] to i32
; CHECK-NEXT: [[R:%.*]] = icmp ne i32 [[TMP1]], 1
; CHECK-NEXT: ret i1 [[R]]
;
%p = getelementptr [4 x %Foo], [4 x %Foo]* @GStructArr, i32 0, i64 %x, i32 2