[PATCH] Allow speculating llvm.sqrt, fma and fmuladd

[Matt Arsenault]

This should be OK since the sqrt intrinsic isn't supposed to be able to set errno, and the standard fma function doesn't anyway. The comment mentions others could be, but the documentation for these is very unclear. sqrt specifically says it doesn't set errno, but the others don't, though it probably shouldn't be different.

http://llvm-reviews.chandlerc.com/D2428

Files:
  lib/Analysis/ValueTracking.cpp
  test/Transforms/SimplifyCFG/speculate-math.ll

Index: lib/Analysis/ValueTracking.cpp
===================================================================
--- lib/Analysis/ValueTracking.cpp
+++ lib/Analysis/ValueTracking.cpp
@@ -2035,6 +2035,12 @@
        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?
Index: test/Transforms/SimplifyCFG/speculate-math.ll
===================================================================
--- /dev/null
+++ test/Transforms/SimplifyCFG/speculate-math.ll
@@ -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-NOT: call
+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-NOT: call
+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-NOT: call
+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
+}
+
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