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Fix invariant fdiv hoisting in LICM 

FDiv is replaced with multiplication by reciprocal and invariant
reciprocal is hoisted out of the loop, while multiplication remains
even if invariant.

Switch checks for all invariant operands and only invariant
denominator to fix the issue.

Differential Revision: https://reviews.llvm.org/D48447

llvm-svn: 335411
This commit is contained in:
Stanislav Mekhanoshin 2018-06-23 04:01:28 +00:00
parent 96917d7912
commit d8c9374797
2 changed files with 42 additions and 16 deletions
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28
llvm/lib/Transforms/Scalar/LICM.cpp
View File

@ -477,6 +477,20 @@ bool llvm::hoistRegion(DomTreeNode *N, AliasAnalysis *AA, LoopInfo *LI,
continue; continue;
} }
// Try hoisting the instruction out to the preheader. We can only do
// this if all of the operands of the instruction are loop invariant and
// if it is safe to hoist the instruction.
//
if (CurLoop->hasLoopInvariantOperands(&I) &&
canSinkOrHoistInst(I, AA, DT, CurLoop, CurAST, SafetyInfo, ORE) &&
(IsMustExecute ||
isSafeToExecuteUnconditionally(
I, DT, CurLoop, SafetyInfo, ORE,
CurLoop->getLoopPreheader()->getTerminator()))) {
Changed |= hoist(I, DT, CurLoop, SafetyInfo, ORE);
continue;
}
// Attempt to remove floating point division out of the loop by // Attempt to remove floating point division out of the loop by
// converting it to a reciprocal multiplication. // converting it to a reciprocal multiplication.
if (I.getOpcode() == Instruction::FDiv && if (I.getOpcode() == Instruction::FDiv &&
@ -500,20 +514,6 @@ bool llvm::hoistRegion(DomTreeNode *N, AliasAnalysis *AA, LoopInfo *LI,
continue; continue;
} }
// Try hoisting the instruction out to the preheader. We can only do
// this if all of the operands of the instruction are loop invariant and
// if it is safe to hoist the instruction.
//
if (CurLoop->hasLoopInvariantOperands(&I) &&
canSinkOrHoistInst(I, AA, DT, CurLoop, CurAST, SafetyInfo, ORE) &&
(IsMustExecute ||
isSafeToExecuteUnconditionally(
I, DT, CurLoop, SafetyInfo, ORE,
CurLoop->getLoopPreheader()->getTerminator()))) {
Changed |= hoist(I, DT, CurLoop, SafetyInfo, ORE);
continue;
}
if (IsMustExecute) if (IsMustExecute)
IsMustExecute = isGuaranteedToTransferExecutionToSuccessor(&I); IsMustExecute = isGuaranteedToTransferExecutionToSuccessor(&I);
} }

30
llvm/test/Transforms/LICM/hoist-fast-fdiv.ll
View File

@ -1,9 +1,9 @@
; RUN: opt -licm -S < %s | FileCheck %s ; RUN: opt -licm -S < %s | FileCheck %s
; Function Attrs: noinline norecurse nounwind readnone ssp uwtable ; Function Attrs: noinline norecurse nounwind readnone ssp uwtable
define zeroext i1 @f(double %v) #0 { define zeroext i1 @invariant_denom(double %v) #0 {
entry: entry:
; CHECK-LABEL: @f( ; CHECK-LABEL: @invariant_denom(
; CHECK-NEXT: entry: ; CHECK-NEXT: entry:
; CHECK-NEXT: fdiv fast double 1.000000e+00, %v ; CHECK-NEXT: fdiv fast double 1.000000e+00, %v
br label %loop br label %loop
@ -32,3 +32,29 @@ end: ; preds = %loop
ret i1 %v16 ret i1 %v16
} }
define void @invariant_fdiv(float* %out, float %arg) {
; CHECK-LABEL: @invariant_fdiv(
; CHECK-NEXT: entry:
; CHECK-NEXT: %div = fdiv fast float 4.000000e+00, %arg
; CHECK-NEXT: fmul fast float %div, 0x41F0000000000000
entry:
br label %loop
loop: ; preds = %loop, %entry
%ind = phi i32 [ 0, %entry ], [ %inc, %loop ]
; CHECK-LABEL: loop:
; CHECK: getelementptr
; CHECK-NOT: fdiv
; CHECK-NOT: fmul
%div = fdiv fast float 4.000000e+00, %arg
%mul = fmul fast float %div, 0x41F0000000000000
%gep = getelementptr inbounds float, float* %out, i32 %ind
store float %mul, float* %gep, align 4
%inc = add nuw nsw i32 %ind, 1
%cond = icmp eq i32 %inc, 1024
br i1 %cond, label %exit, label %loop
exit: ; preds = %loop
ret void
}