[DebugInfo] Maintain DI when converting GEP to bitcast

[ergawy]

Summary

When a GEP with all zero indices is converted to bitcast, its DI wasn't
copied over to the newly created instruction. This patch fixes that bug.

[vsk]

LGTM. Thanks!

lib/CodeGen/CodeGenPrepare.cpp

if (BinOp && (BinOp->getOpcode() == Instruction::AShr ||
     return false;
   }
 
   if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(I)) {
     if (GEPI->hasAllZeroIndices()) {
       /// The GEP operand must be a pointer, so must its result -> BitCast
       Instruction *NC = new BitCastInst(GEPI->getOperand(0), GEPI->getType(),
                                         GEPI->getName(), GEPI);
+      NC->setDebugLoc(GEPI->getDebugLoc());
       GEPI->replaceAllUsesWith(NC);
       GEPI->eraseFromParent();
       ++NumGEPsElim;
       optimizeInst(NC, ModifiedDT);
       return true;
     }
     if (tryUnmergingGEPsAcrossIndirectBr(GEPI, TTI)) {
       return true;

test/DebugInfo/X86/bitcast-di.ll

 ; RUN: opt -mtriple=x86_64-unknown-linux-gnu -S -debugify -codegenprepare < %s | FileCheck %s
 
 target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128"
 target triple = "x86_64-unknown-linux-gnu"
 
+@x = external global [1 x [2 x <4 x float>]]
+
 declare void @foo(i32)
 
 declare void @slowpath(i32, i32*)
 
 ; Is DI maintained after sinking bitcast?
 define void @test(i1 %cond, i64* %base) {
 ; CHECK-LABEL: @test
 entry:

 
 rare.1:
 ; CHECK-LABEL: rare.1:
 ; CHECK: bitcast i64* %addr to i32*, !dbg ![[castLoc]]
   call void @slowpath(i32 %v1, i32* %casted) ;; NOT COLD
   br label %fallthrough
 }
 
+; Is DI maitained when a GEP with all zero indices gets converted to bitcast?
+define void @test2() {
+; CHECK-LABEL: @test2
+load.i145:
+; CHECK: bitcast [1 x [2 x <4 x float>]]* @x to [2 x <4 x float>]*, !dbg ![[castLoc2:[0-9]+]]
+  %x_offset = getelementptr [1 x [2 x <4 x float>]], [1 x [2 x <4 x float>]]* @x, i32 0, i64 0
+  ret void
+}
+
 ; CHECK: ![[castLoc]] = !DILocation(line: 2
+; CHECK: ![[castLoc2]] = !DILocation(line: 11
 No newline at end of file