Approved by Chris:

$ svn merge -c 113257 https://llvm.org/svn/llvm-project/llvm/trunk
--- Merging r113257 into '.':
A    test/Transforms/InstCombine/sqrt.ll
D    test/Transforms/InstCombine/2010-07-19-sqrt.ll

Renaming test.

$ svn merge -c 113260 https://llvm.org/svn/llvm-project/llvm/trunk
--- Merging r113260 into '.':
U    test/Transforms/InstCombine/sqrt.ll
U    lib/Transforms/InstCombine/InstCombineCasts.cpp

Log:
Fix a serious performance regression introduced by r108687 on linux:
turning (fptrunc (sqrt (fpext x))) -> (sqrtf x)  is great, but we have
to delete the original sqrt as well.  Not doing so causes us to do 
two sqrt's when building with -fmath-errno (the default on linux).

llvm-svn: 113265

Author: isanbard

llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp

@@ -1139,14 +1139,19 @@ Instruction *InstCombiner::visitFPTrunc(FPTruncInst &CI) {
         Arg->getOperand(0)->getType()->isFloatTy()) {
       Function *Callee = Call->getCalledFunction();
       Module *M = CI.getParent()->getParent()->getParent();
-      Constant* SqrtfFunc = M->getOrInsertFunction("sqrtf", 
+      Constant *SqrtfFunc = M->getOrInsertFunction("sqrtf", 
                                                    Callee->getAttributes(),
                                                    Builder->getFloatTy(),
                                                    Builder->getFloatTy(),
                                                    NULL);
       CallInst *ret = CallInst::Create(SqrtfFunc, Arg->getOperand(0),
                                        "sqrtfcall");
       ret->setAttributes(Callee->getAttributes());
+      
+      
+      // Remove the old Call.  With -fmath-errno, it won't get marked readnone.
+      Call->replaceAllUsesWith(UndefValue::get(Call->getType()));
+      EraseInstFromFunction(*Call);
       return ret;
     }
   }

llvm/test/Transforms/InstCombine/2010-07-19-sqrt.ll

@@ -0,0 +1,32 @@
+; RUN: opt -S -instcombine %s | FileCheck %s
+
+define float @test1(float %x) nounwind readnone ssp {
+entry:
+; CHECK: @test1
+; CHECK-NOT: fpext
+; CHECK-NOT: sqrt(
+; CHECK: sqrtf(
+; CHECK-NOT: fptrunc
+  %conv = fpext float %x to double                ; <double> [#uses=1]
+  %call = tail call double @sqrt(double %conv) readnone nounwind ; <double> [#uses=1]
+  %conv1 = fptrunc double %call to float          ; <float> [#uses=1]
+; CHECK: ret float
+  ret float %conv1
+}
+
+declare double @sqrt(double)
+
+; PR8096
+define float @test2(float %x) nounwind readnone ssp {
+entry:
+; CHECK: @test2
+; CHECK-NOT: fpext
+; CHECK-NOT: sqrt(
+; CHECK: sqrtf(
+; CHECK-NOT: fptrunc
+  %conv = fpext float %x to double                ; <double> [#uses=1]
+  %call = tail call double @sqrt(double %conv) nounwind ; <double> [#uses=1]
+  %conv1 = fptrunc double %call to float          ; <float> [#uses=1]
+; CHECK: ret float
+  ret float %conv1
+}