[llvm] [AMDGPU][GIsel] Properly handle unsupported intrinsic translation (PR #228040)

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<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-amdgpu

Author: Vikram Hegde (vikramRH)

<details>
<summary>Changes</summary>

unsupported intrinsic results are defined with G_IMPLICIT_DEF, preventing malformed translation.  Basically tries to mimic SDAG path which creates poison results. prerequisite to https://github.com/llvm/llvm-project/pull/227607.

Assisted by: Opus 5



---
Full diff: https://github.com/llvm/llvm-project/pull/228040.diff


2 Files Affected:

- (modified) llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp (+22-10) 
- (modified) llvm/test/CodeGen/AMDGPU/s-wakeup-barrier.ll (+4) 


``````````diff
diff --git a/llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp b/llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp
index 9f043a6f57872..8de42022f84be 100644
--- a/llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp
@@ -337,6 +337,11 @@ class IRTranslatorImpl {
       const CallBase &CB, Intrinsic::ID ID, MachineIRBuilder &MIRBuilder,
       ArrayRef<TargetLowering::IntrinsicInfo> TgtMemIntrinsicInfos = {});
 
+  /// Report an intrinsic the subtarget does not support and define its results
+  /// with G_IMPLICIT_DEF. Prevents creating a malformed MIR.
+  bool handleUnsupportedIntrinsic(const CallBase &CB, Intrinsic::ID ID,
+                                  MachineIRBuilder &MIRBuilder);
+
   /// When an invoke or a cleanupret unwinds to the next EH pad, there are
   /// many places it could ultimately go. In the IR, we have a single unwind
   /// destination, but in the machine CFG, we enumerate all the possible blocks.
@@ -3664,11 +3669,8 @@ bool IRTranslatorImpl::translateCall(const User &U,
 
   assert(ID != Intrinsic::not_intrinsic && "unknown intrinsic");
 
-  if (!MF->getSubtarget().isIntrinsicSupported(ID)) {
-    const Function &Fn = MF->getFunction();
-    Fn.getContext().diagnose(
-        DiagnosticInfoUnsupportedTargetIntrinsic(Fn, ID, CI.getDebugLoc()));
-  }
+  if (!MF->getSubtarget().isIntrinsicSupported(ID))
+    return handleUnsupportedIntrinsic(CI, ID, MIRBuilder);
 
   if (translateKnownIntrinsic(CI, ID, MIRBuilder))
     return true;
@@ -3679,15 +3681,25 @@ bool IRTranslatorImpl::translateCall(const User &U,
   return translateIntrinsic(CI, ID, MIRBuilder, Infos);
 }
 
+bool IRTranslatorImpl::handleUnsupportedIntrinsic(
+    const CallBase &CB, Intrinsic::ID ID, MachineIRBuilder &MIRBuilder) {
+  const Function &F = MF->getFunction();
+  F.getContext().diagnose(
+      DiagnosticInfoUnsupportedTargetIntrinsic(F, ID, CB.getDebugLoc()));
+
+  if (!CB.getType()->isVoidTy())
+    for (Register Reg : getOrCreateVRegs(CB))
+      MIRBuilder.buildUndef(Reg);
+
+  return true;
+}
+
 /// Translate a call or callbr to an intrinsic.
 bool IRTranslatorImpl::translateIntrinsic(
     const CallBase &CB, Intrinsic::ID ID, MachineIRBuilder &MIRBuilder,
     ArrayRef<TargetLowering::IntrinsicInfo> TgtMemIntrinsicInfos) {
-  if (!MF->getSubtarget().isIntrinsicSupported(ID)) {
-    const Function &F = MF->getFunction();
-    F.getContext().diagnose(
-        DiagnosticInfoUnsupportedTargetIntrinsic(F, ID, CB.getDebugLoc()));
-  }
+  if (!MF->getSubtarget().isIntrinsicSupported(ID))
+    return handleUnsupportedIntrinsic(CB, ID, MIRBuilder);
 
   ArrayRef<Register> ResultRegs;
   if (!CB.getType()->isVoidTy())
diff --git a/llvm/test/CodeGen/AMDGPU/s-wakeup-barrier.ll b/llvm/test/CodeGen/AMDGPU/s-wakeup-barrier.ll
index 192c8b4d95039..bf108456b8bab 100644
--- a/llvm/test/CodeGen/AMDGPU/s-wakeup-barrier.ll
+++ b/llvm/test/CodeGen/AMDGPU/s-wakeup-barrier.ll
@@ -5,6 +5,10 @@
 ; RUN: not llc -global-isel=0 -mtriple=amdgpu12.00 -filetype=null < %s 2>&1 | FileCheck -check-prefix=ERR %s
 ; RUN: not llc -global-isel=1 -mtriple=amdgpu12.00 -filetype=null < %s 2>&1 | FileCheck -check-prefix=ERR %s
 
+; Check that we report the error rather than crashing on pre-gfx12.
+; RUN: not llc -global-isel=0 -mtriple=amdgpu9.42 -filetype=null < %s 2>&1 | FileCheck -check-prefix=ERR %s
+; RUN: not llc -global-isel=1 -mtriple=amdgpu9.42 -filetype=null < %s 2>&1 | FileCheck -check-prefix=ERR %s
+
 ; ERR: error: <unknown>:0:0: in function @kernel1 void (ptr addrspace(1), ptr addrspace(15)): llvm.amdgcn.s.wakeup.barrier requires target feature 's-wakeup-barrier-inst'
 
 @bar = internal addrspace(15) global target("amdgcn.named.barrier", 0) poison

``````````

</details>


https://github.com/llvm/llvm-project/pull/228040