[PartiallyInlineLibCalls] Disable sqrt expansion for strictfp.

[craig.topper]

Summary

This pass emits a floating point compare and a conditional branch,
but if strictfp is enabled we don't emit a constrained compare
intrinsic.

The backend also won't expand the readonly sqrt call this pass inserts
to a sqrt instruction under strictfp. So we end up with 2 libcalls as
seen here. https://godbolt.org/z/oax5zMEWd

Fix these things by disabling the pass.

[kpn]

llvm/test/Transforms/PartiallyInlineLibCalls/strictfp.ll

5

I'm pretty sure this needs the strictfp attribute as well.

9

There is a constrained sqrt. It seems like not emitting it is the real bug.

[craig.topper]

llvm/test/Transforms/PartiallyInlineLibCalls/strictfp.ll

9

From the frontend?

[craig.topper]

Add strictfp to caller in test case.

[kpn]

llvm/test/Transforms/PartiallyInlineLibCalls/strictfp.ll

9

A quick check shows that we actually are emitting the constrained sqrt call from clang, at least we are using the arguments from the godbolt link. So I'm not sure how we got here?

[craig.topper]

llvm/test/Transforms/PartiallyInlineLibCalls/strictfp.ll

9

We can only emit an intrinsic call if -fno-math-errno is in effect. If we need errno, we must call the library function.

[craig.topper]

llvm/test/Transforms/PartiallyInlineLibCalls/strictfp.ll

9

The goal of this pass is to fast path the handling of sane inputs that aren't an error condition and fall back to libcall to get errno updated if we detect a bad input.

[kpn]

Ah, errno. That was the missing piece. Got it.

LGTM

llvm/lib/Transforms/Scalar/PartiallyInlineLibCalls.cpp

for (Function::iterator BB = F.begin(), BE = F.end(); BB != BE;) {
     for (BasicBlock::iterator II = CurrBB->begin(), IE = CurrBB->end();
          II != IE; ++II) {
       CallInst *Call = dyn_cast<CallInst>(&*II);
       Function *CalledFunc;
 
       if (!Call || !(CalledFunc = Call->getCalledFunction()))
         continue;
 
-      if (Call->isNoBuiltin())
+      if (Call->isNoBuiltin() || Call->isStrictFP())
         continue;
 
       // Skip if function either has local linkage or is not a known library
       // function.
       LibFunc LF;
       if (CalledFunc->hasLocalLinkage() ||
           !TLI->getLibFunc(*CalledFunc, LF) || !TLI->has(LF))
         continue;

llvm/test/Transforms/PartiallyInlineLibCalls/strictfp.ll

+; RUN: opt -S -partially-inline-libcalls -mtriple=x86_64-unknown-linux-gnu < %s | FileCheck %s
+; RUN: opt -S -passes=partially-inline-libcalls -mtriple=x86_64-unknown-linux-gnu < %s | FileCheck %s
+
+define float @f(float %val) strictfp {
+; CHECK-LABEL: @f
+; CHECK: call{{.*}}@sqrtf
+; CHECK-NOT: call{{.*}}@sqrtf
+  %res = tail call float @sqrtf(float %val) strictfp
+  ret float %res
+}
+
+declare float @sqrtf(float)