Don't partially inline a musttail libcall.

[babrath]

Summary

Partially inlining a libcall that has the musttail attribute leads to broken LLVM IR, triggering an assertion in the IR verifier. Compiling this file with -O2 -c should trigger the assertion. The proposed changes fix the issue, although I'm not 100% certain simply forgoing the optimization for musttail calls is the proper approach.

test.c89 BDownload

[lebedev.ri]

Test?

[babrath]

In D123116#3429087, @lebedev.ri wrote:

Test?

Compiling the attached file with the mentioned flags triggers the assertion without the patch, and compiles correctly with the patch. Or does it need to come in a specific form? It's my first time suggesting a patch.

[xbolva00]

Some simple llc test for X86 (llvm/test/CodeGen/X86/) could work fine here:
https://godbolt.org/z/czTzMvx1r

; RUN: llc < %s -mtriple=x86_64-unknown-unknown | FileCheck %s

[babrath]

Adding test, using opt instead of llc.

[lebedev.ri]

llvm/test/Transforms/PartiallyInlineLibCalls/musttail.ll

1 ↗

(On Diff #420490)

Please put the file into X86/ dir, and use the utils/update_test_checks.py script to autogenerate check lines.

[babrath]

Moving test to X86, updating with update_test_checks.py.

[lebedev.ri]

LG.
Please specify the "Name <[e-mail]>" to be used for commit.

[babrath]

In D123116#3429522, @lebedev.ri wrote:

LG.
Please specify the "Name <[e-mail]>" to be used for commit.

That would be "Bert Abrath <[e-mail]>". Unless I actually have to add that somewhere? Thanks for all the help :-)

llvm/lib/Transforms/Scalar/PartiallyInlineLibCalls.cpp

for (BasicBlock::iterator II = CurrBB->begin(), IE = CurrBB->end();
       Function *CalledFunc;
 
       if (!Call || !(CalledFunc = Call->getCalledFunction()))
         continue;
 
       if (Call->isNoBuiltin() || Call->isStrictFP())
         continue;
 
+      if (Call->isMustTailCall())
+        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;
 
       switch (LF) {

llvm/test/Transforms/PartiallyInlineLibCalls/X86/musttail.ll

+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; 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 double @foo(double %x) {
+; CHECK-LABEL: @foo(
+; CHECK-NEXT:    [[R:%.*]] = musttail call double @sqrt(double [[X:%.*]])
+; CHECK-NEXT:    ret double [[R]]
+;
+  %r = musttail call double @sqrt(double %x)
+  ret double %r
+}
+
+declare double @sqrt(double)