Fix out-of-order stepping behavior in programs with hoisted constants.

When the Constant Hoisting pass moves expensive constants into a
common block, it would assign a debug location equal to the last use
of that constant. While this is certainly intuitive, it places the
constant in an out-of-order location, according to the debug location
information. This produces out-of-order stepping when debugging
programs affected by this pass.

This patch creates in-order stepping behavior by merging the debug
locations for hoisted constants, and the new insertion point.

Patch by Matthew Voss!

Differential Revision: https://reviews.llvm.org/D38088

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@317827 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Scalar/ConstantHoisting.cpp

@@ -60,6 +60,7 @@
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/Transforms/Scalar.h"
 #include "llvm/Transforms/Utils/Local.h"
+#include "llvm/IR/DebugInfoMetadata.h"
 #include <algorithm>
 #include <cassert>
 #include <cstdint>
@@ -716,6 +717,9 @@ bool ConstantHoistingPass::emitBaseConstants() {
       IntegerType *Ty = ConstInfo.BaseConstant->getType();
       Instruction *Base =
           new BitCastInst(ConstInfo.BaseConstant, Ty, "const", IP);
+
+      Base->setDebugLoc(IP->getDebugLoc());
+
       DEBUG(dbgs() << "Hoist constant (" << *ConstInfo.BaseConstant
                    << ") to BB " << IP->getParent()->getName() << '\n'
                    << *Base << '\n');
@@ -734,6 +738,8 @@ bool ConstantHoistingPass::emitBaseConstants() {
             emitBaseConstants(Base, RCI.Offset, U);
             ReBasesNum++;
           }
+
+          Base->setDebugLoc(DILocation::getMergedLocation(Base->getDebugLoc(), U.Inst->getDebugLoc()));
         }
       }
       UsesNum = Uses;
@@ -742,7 +748,6 @@ bool ConstantHoistingPass::emitBaseConstants() {
       assert(!Base->use_empty() && "The use list is empty!?");
       assert(isa<Instruction>(Base->user_back()) &&
              "All uses should be instructions.");
-      Base->setDebugLoc(cast<Instruction>(Base->user_back())->getDebugLoc());
     }
     (void)UsesNum;
     (void)ReBasesNum;

test/Transforms/ConstantHoisting/X86/dbg-dominatingblock.ll

@@ -0,0 +1,55 @@
+; RUN: opt -S -consthoist < %s | FileCheck %s
+; ModuleID = 'test-hoist-debug.cpp'
+source_filename = "test-hoist-debug.cpp"
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; Function Attrs: noinline nounwind optnone uwtable
+define i32 @_Z3foov() !dbg !7 {
+; CHECK: bitcast
+; CHECK-NOT: !dbg !11
+; CHECK: inttoptr 
+entry:
+  %a0 = inttoptr i64 4646526064 to i32*
+  %v0 = load i32, i32* %a0, align 16, !dbg !11
+  %c = alloca i32, align 4
+  store i32 1, i32* %c, align 4
+  %0 = load i32, i32* %c, align 4
+  %cmp = icmp eq i32 %0, 0
+  br i1 %cmp, label %if.then, label %if.else
+
+if.then:                                          ; preds = %entry
+  %a1 = inttoptr i64 4646526080 to i32*
+  %v1 = load i32, i32* %a1, align 16, !dbg !11
+  br label %return
+
+if.else:                                          ; preds = %entry
+  %a2 = inttoptr i64 4646526096 to i32*
+  %v2 = load i32, i32* %a2, align 16, !dbg !11
+  br label %return
+
+return:                                           ; preds = %if.else, %if.then
+  %vx = phi i32 [%v1, %if.then], [%v2, %if.else]
+  %r0 = add i32 %vx, %v0
+
+  ret i32 %r0
+}
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5}
+!llvm.ident = !{!6}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 6.0.0 (trunk 313291)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "test-hoist-debug.cpp", directory: "/tmp")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 4}
+!6 = !{!"clang version 6.0.0 (trunk 313291)"}
+!7 = distinct !DISubprogram(name: "foo", linkageName: "_Z3foov", scope: !1, file: !1, line: 1, type: !8, isLocal: false, isDefinition: true, scopeLine: 1, flags: DIFlagPrototyped, isOptimized: false, unit: !0, variables: !2)
+!8 = !DISubroutineType(types: !9)
+!9 = !{!10}
+!10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!11 = !DILocation(line: 2, column: 3, scope: !7)
+!12 = !DILocation(line: 3, column: 3, scope: !7)
+!13 = !DILocation(line: 4, column: 3, scope: !7)

test/Transforms/ConstantHoisting/X86/dbg-samebasicblock.ll

@@ -0,0 +1,41 @@
+; RUN: opt -S -consthoist < %s | FileCheck %s
+; ModuleID = 'test-hoist-debug.cpp'
+source_filename = "test-hoist-debug.cpp"
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; Function Attrs: noinline nounwind optnone uwtable
+define i32 @_Z3foov() !dbg !7 {
+; CHECK: bitcast
+; CHECK: !dbg !11
+; CHECK: inttoptr 
+  %a0 = inttoptr i64 4646526064 to i32*, !dbg !11
+  %v0 = load i32, i32* %a0, align 16, !dbg !11
+
+  %a1 = inttoptr i64 4646526080 to i32*
+  %v1 = load i32, i32* %a1, align 16, !dbg !11
+
+  %a2 = inttoptr i64 4646526096 to i32*
+  %v2 = load i32, i32* %a2, align 16, !dbg !11
+
+  %r0 = add i32 %v0, %v1
+  %r1 = add i32 %r0, %v2
+  ret i32 %r1
+}
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5}
+!llvm.ident = !{!6}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 6.0.0 (trunk 313291)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "test-hoist-debug.cpp", directory: "/tmp")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 4}
+!6 = !{!"clang version 6.0.0 (trunk 313291)"}
+!7 = distinct !DISubprogram(name: "foo", linkageName: "_Z3foov", scope: !1, file: !1, line: 1, type: !8, isLocal: false, isDefinition: true, scopeLine: 1, flags: DIFlagPrototyped, isOptimized: false, unit: !0, variables: !2)
+!8 = !DISubroutineType(types: !9)
+!9 = !{!10}
+!10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!11 = !DILocation(line: 2, column: 3, scope: !7)