[MIPS][ISel] Fix musttail

[djtodoro]

Properly handle clang::musttail attribute on MIPS backend.

It fixes: #161193

[llvmbot]

@llvm/pr-subscribers-backend-mips

Author: Djordje Todorovic (djtodoro)

Changes

Properly handle clang::musttail attribute on MIPS backend.

It fixes: #161193

---

Full diff: https://github.com/llvm/llvm-project/pull/161860.diff

2 Files Affected:

• (modified) llvm/lib/Target/Mips/MipsISelLowering.cpp (+4-3)
• (added) llvm/test/CodeGen/Mips/musttail.ll (+38)

diff --git a/llvm/lib/Target/Mips/MipsISelLowering.cpp b/llvm/lib/Target/Mips/MipsISelLowering.cpp
index 881ba8e2f9eff..d79db127f01a2 100644
--- a/llvm/lib/Target/Mips/MipsISelLowering.cpp
+++ b/llvm/lib/Target/Mips/MipsISelLowering.cpp
@@ -3407,7 +3407,8 @@ MipsTargetLowering::LowerCall(TargetLowering::CallLoweringInfo &CLI,
   // Check if it's really possible to do a tail call. Restrict it to functions
   // that are part of this compilation unit.
   bool InternalLinkage = false;
-  if (IsTailCall) {
+  bool IsMustTail = CLI.CB && CLI.CB->isMustTailCall();
+  if (IsTailCall && !IsMustTail) {
     IsTailCall = isEligibleForTailCallOptimization(
         CCInfo, StackSize, *MF.getInfo<MipsFunctionInfo>());
     if (GlobalAddressSDNode *G = dyn_cast<GlobalAddressSDNode>(Callee)) {
@@ -3416,9 +3417,9 @@ MipsTargetLowering::LowerCall(TargetLowering::CallLoweringInfo &CLI,
                      G->getGlobal()->hasPrivateLinkage() ||
                      G->getGlobal()->hasHiddenVisibility() ||
                      G->getGlobal()->hasProtectedVisibility());
-     }
+    }
   }
-  if (!IsTailCall && CLI.CB && CLI.CB->isMustTailCall())
+  if (!IsTailCall && IsMustTail)
     report_fatal_error("failed to perform tail call elimination on a call "
                        "site marked musttail");
 
diff --git a/llvm/test/CodeGen/Mips/musttail.ll b/llvm/test/CodeGen/Mips/musttail.ll
new file mode 100644
index 0000000000000..d5f457f6eb665
--- /dev/null
+++ b/llvm/test/CodeGen/Mips/musttail.ll
@@ -0,0 +1,38 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -mtriple=mips-unknown-linux-gnu < %s | FileCheck %s --check-prefix=MIPS32
+; RUN: llc -mtriple=mips64-unknown-linux-gnu < %s | FileCheck %s --check-prefix=MIPS64
+
+; Test musttail support for MIPS
+
+declare void @external_func()
+
+; Test basic musttail with external function
+define void @test_musttail_external() {
+; MIPS32-LABEL: test_musttail_external:
+; MIPS32:       # %bb.0:
+; MIPS32-NEXT:    j external_func
+; MIPS32-NEXT:    nop
+;
+; MIPS64-LABEL: test_musttail_external:
+; MIPS64:       # %bb.0:
+; MIPS64-NEXT:    j external_func
+; MIPS64-NEXT:    nop
+  musttail call void @external_func()
+  ret void
+}
+
+declare i32 @callee_args(i32 %a, i32 %b, i32 %c)
+
+define i32 @test_musttail_args(i32 %x, i32 %y, i32 %z) {
+; MIPS32-LABEL: test_musttail_args:
+; MIPS32:       # %bb.0:
+; MIPS32-NEXT:    j callee_args
+; MIPS32-NEXT:    nop
+;
+; MIPS64-LABEL: test_musttail_args:
+; MIPS64:       # %bb.0:
+; MIPS64-NEXT:    j callee_args
+; MIPS64-NEXT:    nop
+  %ret = musttail call i32 @callee_args(i32 %x, i32 %y, i32 %z)
+  ret i32 %ret
+}

[kraj]

LGTM

[jrtc27]

Uh don't we still need to check it's eligible?

[djtodoro]

Well, that thing confuses me in the case of musttail. On ARM, we do check it. Lets do it for MIPS as well.

[djtodoro]

@jrtc27 yep, it does make sense to still check it. I incorporated in the new commit (basically - do not check for the optional mips flag for enabling tail call optimizations in case of musttial, and I also enabled tail call opts for dso_local functions (1dcb9110612ab) ). Thanks for the review!

[jrtc27]

.

[djtodoro]

I checked the issues listed above, all cases from those still pass with the new patch.

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[kraj]

Please squash changes into initial commit

[djtodoro]

Please squash changes into initial commit

Per "Contributing to LLVM" Policy, we do not do force-push (and squash), we rather use incremental changes to address comments during review process. And, once the pull request is approved, we select the “Squash and merge” button.

[kraj]

my checks pass with this series as well.

[kraj]

Please squash changes into initial commit

Per "Contributing to LLVM" Policy, we do not do force-push (and squash), we rather use incremental changes to address comments during review process. And, once the pull request is approved, we select the “Squash and merge” button.

right, squashing is what I meant.

[djtodoro]

I will wait for @jrtc27 to have another look. :)

[brad0]

@jrtc27 @yingopq Ping.