[GlobalISel][IRTranslator] Use RPO traversal when visiting blocks to translate.

Previously we were just visiting the blocks in the function in IR order, which
is rather arbitrary. Therefore we wouldn't always visit defs before uses, but
the translation code relies on this assumption in some places.

Only codegen change seen in tests is an elision of a redundant copy.

Fixes PR38396

llvm-svn: 338476

1 files changed, 8 insertions, 5 deletions

diff --git a/llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp b/llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp
index e76c40f8d93..80da50562d3 100644
--- a/llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp
@@ -11,6 +11,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/CodeGen/GlobalISel/IRTranslator.h"
+#include "llvm/ADT/PostOrderIterator.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/ScopeExit.h"
 #include "llvm/ADT/SmallSet.h"
@@ -33,6 +34,7 @@
 #include "llvm/CodeGen/TargetRegisterInfo.h"
 #include "llvm/CodeGen/TargetSubtargetInfo.h"
 #include "llvm/IR/BasicBlock.h"
+#include "llvm/IR/CFG.h"
 #include "llvm/IR/Constant.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/DataLayout.h"
@@ -1613,19 +1615,20 @@ bool IRTranslator::runOnMachineFunction(MachineFunction &CurMF) {
     ArgIt++;
   }
 
-  // And translate the function!
-  for (const BasicBlock &BB : F) {
-    MachineBasicBlock &MBB = getMBB(BB);
+  // Need to visit defs before uses when translating instructions.
+  ReversePostOrderTraversal<const Function *> RPOT(&F);
+  for (const BasicBlock *BB : RPOT) {
+    MachineBasicBlock &MBB = getMBB(*BB);
     // Set the insertion point of all the following translations to
     // the end of this basic block.
     CurBuilder.setMBB(MBB);
 
-    for (const Instruction &Inst : BB) {
+    for (const Instruction &Inst : *BB) {
       if (translate(Inst))
         continue;
 
       OptimizationRemarkMissed R("gisel-irtranslator", "GISelFailure",
-                                 Inst.getDebugLoc(), &BB);
+                                 Inst.getDebugLoc(), BB);
       R << "unable to translate instruction: " << ore::NV("Opcode", &Inst);
 
       if (ORE->allowExtraAnalysis("gisel-irtranslator")) {