[GlobalISel][IRTranslator] Support PHI instructions in landingpad blocks

[kschwarz]

Summary

The check for the landingpad instructions was overly restrictive. In optimimized builds PHI nodes can appear
before the landingpad instructions, resulting in a fallback to SelectionDAG.

This change relaxes the check to allow PHI nodes.

[arsenm]

llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp

2032

Is the fixme still relevant?

[arsenm]

llvm/test/CodeGen/AArch64/GlobalISel/irtranslator-exceptions.ll

128

Is it legal to have debug info before the landing pad? If so can you add a test with that in the way too?

[kschwarz]

llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp

2032

I think so. Windows uses catchswitch/catchpad instructions for exception handling AFAIK, which aren't handled yet.

llvm/test/CodeGen/AArch64/GlobalISel/irtranslator-exceptions.ll

128

Seems its not legal. From LangRef:

[...] ‘exception’ label is required to have the “landingpad” instruction, which contains the information about the behavior of the program after unwinding happens, as its first non-PHI instruction.

llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp

bool IRTranslator::translateInvoke(const User &U,
   // FIXME: support whatever these are.
   if (I.countOperandBundlesOfType(LLVMContext::OB_deopt))
     return false;
 
   // FIXME: support control flow guard targets.
   if (I.countOperandBundlesOfType(LLVMContext::OB_cfguardtarget))
     return false;
 
   // FIXME: support Windows exception handling.
-  if (!isa<LandingPadInst>(EHPadBB->front()))
+  if (!isa<LandingPadInst>(EHPadBB->getFirstNonPHI()))
     return false;
 
   // Emit the actual call, bracketed by EH_LABELs so that the MF knows about
   // the region covered by the try.
   MCSymbol *BeginSymbol = Context.createTempSymbol();
   MIRBuilder.buildInstr(TargetOpcode::EH_LABEL).addSym(BeginSymbol);
 
   if (!translateCallBase(I, MIRBuilder))

llvm/test/CodeGen/AArch64/GlobalISel/irtranslator-exceptions.ll

 
 broken:
   landingpad { i8*, i32 } catch i8* bitcast(i8** @_ZTIi to i8*)
   ret void
 
 continue:
   ret void
 }
+
+; CHECK-LABEL: name: test_lpad_phi
+; CHECK: body:
+; CHECK-NEXT:   bb.1 (%ir-block.0):
+; CHECK:     successors: %[[GOOD:bb.[0-9]+]]{{.*}}%[[BAD:bb.[0-9]+]]
+; CHECK:     [[ELEVEN:%[0-9]+]]:_(s32) = G_CONSTANT i32 11
+; CHECK:     EH_LABEL
+; CHECK:     BL @may_throw, csr_darwin_aarch64_aapcs, implicit-def $lr, implicit $sp
+; CHECK:     EH_LABEL
+; CHECK:     G_BR %[[GOOD]]
+
+; CHECK:   [[BAD]].{{[a-z]+}} (landing-pad):
+; CHECK:     [[PHI_ELEVEN:%[0-9]+]]:_(s32) = G_PHI [[ELEVEN]](s32), %bb.1
+; CHECK:     EH_LABEL
+; CHECK:     G_STORE [[PHI_ELEVEN]](s32), {{%[0-9]+}}(p0) :: (store 4 into @global_var)
+
+; CHECK:   [[GOOD]].{{[a-z]+}}:
+; CHECK:     [[SEL:%[0-9]+]]:_(s32) = G_PHI
+; CHECK:     $w0 = COPY [[SEL]]
+
+@global_var = external global i32
+
+declare void @may_throw()
+define i32 @test_lpad_phi() personality i8* bitcast (i32 (...)* @__gxx_personality_v0 to i8*) {
+  store i32 42, i32* @global_var
+  invoke void @may_throw()
+          to label %continue unwind label %lpad
+
+lpad:                                             ; preds = %entry
+  %p = phi i32 [ 11, %0 ]  ; Trivial, but -O0 keeps it
+  %1 = landingpad { i8*, i32 }
+          catch i8* null
+  store i32 %p, i32* @global_var
+  br label %continue
+
+continue:                                         ; preds = %entry, %lpad
+  %r.0 = phi i32 [ 13, %0 ], [ 55, %lpad ]
+  ret i32 %r.0
+}