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Allow speculating llvm.sqrt, fma and fmuladd

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This doesn't set errno, so this should be OK.
Also update the documentation to explicitly state
that errno are not set.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@200501 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Matt Arsenault 2014-01-31 00:09:00 +00:00
parent 4b4b808860
commit e932091eb5
3 changed files with 67 additions and 2 deletions
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5
docs/LangRef.rst
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@ -7490,7 +7490,7 @@ Semantics:
""""""""""
This function returns the same values as the libm ``fma`` functions
would.
would, and does not set errno.
'``llvm.fabs.*``' Intrinsic
^^^^^^^^^^^^^^^^^^^^^^^^^^^
@ -8298,7 +8298,8 @@ is equivalent to the expression a \* b + c, except that rounding will
not be performed between the multiplication and addition steps if the
code generator fuses the operations. Fusion is not guaranteed, even if
the target platform supports it. If a fused multiply-add is required the
corresponding llvm.fma.\* intrinsic function should be used instead.
corresponding llvm.fma.\* intrinsic function should be used
instead. This never sets errno, just as '``llvm.fma.*``'.
Examples:
"""""""""

6
lib/Analysis/ValueTracking.cpp
View File

@ -2036,6 +2036,12 @@ bool llvm::isSafeToSpeculativelyExecute(const Value *V,
case Intrinsic::umul_with_overflow:
case Intrinsic::usub_with_overflow:
return true;
// Sqrt should be OK, since the llvm sqrt intrinsic isn't defined to set
// errno like libm sqrt would.
case Intrinsic::sqrt:
case Intrinsic::fma:
case Intrinsic::fmuladd:
return true;
// TODO: some fp intrinsics are marked as having the same error handling
// as libm. They're safe to speculate when they won't error.
// TODO: are convert_{from,to}_fp16 safe?

58
test/Transforms/SimplifyCFG/speculate-math.ll Normal file
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@ -0,0 +1,58 @@
; RUN: opt -S -simplifycfg -phi-node-folding-threshold=2 < %s | FileCheck %s
declare float @llvm.sqrt.f32(float) nounwind readonly
declare float @llvm.fma.f32(float, float, float) nounwind readonly
declare float @llvm.fmuladd.f32(float, float, float) nounwind readonly
; CHECK-LABEL: @sqrt_test(
; CHECK: select
define void @sqrt_test(float addrspace(1)* noalias nocapture %out, float %a) nounwind {
entry:
%cmp.i = fcmp olt float %a, 0.000000e+00
br i1 %cmp.i, label %test_sqrt.exit, label %cond.else.i
cond.else.i: ; preds = %entry
%0 = tail call float @llvm.sqrt.f32(float %a) nounwind readnone
br label %test_sqrt.exit
test_sqrt.exit: ; preds = %cond.else.i, %entry
%cond.i = phi float [ %0, %cond.else.i ], [ 0x7FF8000000000000, %entry ]
store float %cond.i, float addrspace(1)* %out, align 4
ret void
}
; CHECK-LABEL: @fma_test(
; CHECK: select
define void @fma_test(float addrspace(1)* noalias nocapture %out, float %a, float %b, float %c) nounwind {
entry:
%cmp.i = fcmp olt float %a, 0.000000e+00
br i1 %cmp.i, label %test_fma.exit, label %cond.else.i
cond.else.i: ; preds = %entry
%0 = tail call float @llvm.fma.f32(float %a, float %b, float %c) nounwind readnone
br label %test_fma.exit
test_fma.exit: ; preds = %cond.else.i, %entry
%cond.i = phi float [ %0, %cond.else.i ], [ 0x7FF8000000000000, %entry ]
store float %cond.i, float addrspace(1)* %out, align 4
ret void
}
; CHECK-LABEL: @fmuladd_test(
; CHECK: select
define void @fmuladd_test(float addrspace(1)* noalias nocapture %out, float %a, float %b, float %c) nounwind {
entry:
%cmp.i = fcmp olt float %a, 0.000000e+00
br i1 %cmp.i, label %test_fmuladd.exit, label %cond.else.i
cond.else.i: ; preds = %entry
%0 = tail call float @llvm.fmuladd.f32(float %a, float %b, float %c) nounwind readnone
br label %test_fmuladd.exit
test_fmuladd.exit: ; preds = %cond.else.i, %entry
%cond.i = phi float [ %0, %cond.else.i ], [ 0x7FF8000000000000, %entry ]
store float %cond.i, float addrspace(1)* %out, align 4
ret void
}