[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

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@338476 91177308-0d34-0410-b5e6-96231b3b80d8

Author: aemerson

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"
@@ -32,6 +33,7 @@
 #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"
@@ -1593,19 +1595,20 @@ 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")) {

test/CodeGen/AArch64/GlobalISel/arm64-fallback.ll

@@ -141,7 +141,7 @@ define fp128 @test_quad_dump() {
   ret fp128 0xL00000000000000004000000000000000
 }
 
-; FALLBACK-WITH-REPORT-ERR: remark: <unknown>:0:0: unable to legalize instruction: %0:_(p0) = G_EXTRACT_VECTOR_ELT %1:_(<2 x p0>), %2:_(s32) (in function: vector_of_pointers_extractelement)
+; FALLBACK-WITH-REPORT-ERR: remark: <unknown>:0:0: unable to legalize instruction: %2:_(p0) = G_EXTRACT_VECTOR_ELT %0:_(<2 x p0>), %3:_(s32) (in function: vector_of_pointers_extractelement)
 ; FALLBACK-WITH-REPORT-ERR: warning: Instruction selection used fallback path for vector_of_pointers_extractelement
 ; FALLBACK-WITH-REPORT-OUT-LABEL: vector_of_pointers_extractelement:
 @var = global <2 x i16*> zeroinitializer
@@ -158,7 +158,7 @@ end:
   br label %block
 }
 
-; FALLBACK-WITH-REPORT-ERR: remark: <unknown>:0:0: unable to legalize instruction: G_STORE %0:_(<2 x p0>), %5:_(p0) :: (store 16 into `<2 x i16*>* undef`) (in function: vector_of_pointers_insertelement)
+; FALLBACK-WITH-REPORT-ERR: remark: <unknown>:0:0: unable to legalize instruction: G_STORE %2:_(<2 x p0>), %1:_(p0) :: (store 16 into `<2 x i16*>* undef`) (in function: vector_of_pointers_insertelement)
 ; FALLBACK-WITH-REPORT-ERR: warning: Instruction selection used fallback path for vector_of_pointers_insertelement
 ; FALLBACK-WITH-REPORT-OUT-LABEL: vector_of_pointers_insertelement:
 define void @vector_of_pointers_insertelement() {

test/CodeGen/AArch64/GlobalISel/arm64-irtranslator.ll

@@ -138,9 +138,9 @@ false:
 ; CHECK: %0:_(s32) = COPY $w0
 ; CHECK: %[[reg100:[0-9]+]]:_(s32) = G_CONSTANT i32 100
 ; CHECK: %[[reg200:[0-9]+]]:_(s32) = G_CONSTANT i32 200
-; CHECK: %[[reg0:[0-9]+]]:_(s32) = G_CONSTANT i32 0
-; CHECK: %[[reg1:[0-9]+]]:_(s32) = G_CONSTANT i32 1
 ; CHECK: %[[reg2:[0-9]+]]:_(s32) = G_CONSTANT i32 2
+; CHECK: %[[reg1:[0-9]+]]:_(s32) = G_CONSTANT i32 1
+; CHECK: %[[reg0:[0-9]+]]:_(s32) = G_CONSTANT i32 0
 ; CHECK: %[[regicmp100:[0-9]+]]:_(s1) = G_ICMP intpred(eq), %[[reg100]](s32), %0
 ; CHECK: G_BRCOND %[[regicmp100]](s1), %[[BB_CASE100]]
 ; CHECK: G_BR %[[BB_NOTCASE100_CHECKNEXT]]
@@ -413,9 +413,9 @@ define i64* @trivial_bitcast(i8* %a) {
 ; CHECK:     G_BR %[[CAST:bb\.[0-9]+]]
 
 ; CHECK: [[END:bb\.[0-9]+]].{{[a-zA-Z0-9.]+}}:
+; CHECK:     $x0 = COPY [[A]]
 
 ; CHECK: [[CAST]].{{[a-zA-Z0-9.]+}}:
-; CHECK:     {{%[0-9]+}}:_(p0) = COPY [[A]]
 ; CHECK:     G_BR %[[END]]
 define i64* @trivial_bitcast_with_copy(i8* %a) {
   br label %cast

test/CodeGen/AArch64/GlobalISel/irtranslator-block-order.ll

@@ -0,0 +1,19 @@
+; RUN: llc -O0 -o - %s | FileCheck %s
+target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"
+target triple = "aarch64-unknown-linux-gnu"
+
+; CHECK-LABEL: testfn
+; CHECK: ret
+define void @testfn() {
+start:
+  br label %bb2
+
+bb1:
+  store i8 %0, i8* undef, align 4
+  ret void
+
+bb2:
+  %0 = extractvalue { i32, i8 } undef, 1
+  br label %bb1
+}
+