[GVN] Use a simpler form of IRBuilder constructor.

[samsonov]

Summary

A side effect of this change is that it IRBuilder now automatically
created debug info locations for new instructions, which is the
same as debug location of insertion point. This is fine for the
functions in questions (GetStoreValueForLoad and
GetMemInstValueForLoad), as they are used in two situations:

• GVN::processLoad, which tries to eliminate a load. In this case new instructions would have the same debug location as the load they eventually replace;
• MaterializeAdjustedValue, which adds new instructions to the end of the basic blocks, which could later be used to replace the load definition. In this case we don't yet know the way the load would be eventually replaced (either by assembling the precomputed values via PHI, or by using them directly), so just using the basic block strategy seems to be reasonable. There is also a special case in the code that *would* adjust the location of the last instruction replacing the load definition to the location of the load.

[dblaikie]

Looks good to me (Danny might have some thoughts, but can always address them in post commit, etc).

[• dberlin]

LGTM

lib/Transforms/Scalar/GVN.cpp

 static Value *GetStoreValueForLoad(Value *SrcVal, unsigned Offset,
                                    Type *LoadTy,
                                    Instruction *InsertPt, const DataLayout &DL){
   LLVMContext &Ctx = SrcVal->getType()->getContext();
 
   uint64_t StoreSize = (DL.getTypeSizeInBits(SrcVal->getType()) + 7) / 8;
   uint64_t LoadSize = (DL.getTypeSizeInBits(LoadTy) + 7) / 8;
 
-  IRBuilder<> Builder(InsertPt->getParent(), InsertPt);
+  IRBuilder<> Builder(InsertPt);
 
   // Compute which bits of the stored value are being used by the load.  Convert
   // to an integer type to start with.
   if (SrcVal->getType()->getScalarType()->isPointerTy())
     SrcVal = Builder.CreatePtrToInt(SrcVal,
         DL.getIntPtrType(SrcVal->getType()));
   if (!SrcVal->getType()->isIntegerTy())
     SrcVal = Builder.CreateBitCast(SrcVal, IntegerType::get(Ctx, StoreSize*8));

 /// This function is called when we have a
 /// memdep query of a load that ends up being a clobbering mem intrinsic.
 static Value *GetMemInstValueForLoad(MemIntrinsic *SrcInst, unsigned Offset,
                                      Type *LoadTy, Instruction *InsertPt,
                                      const DataLayout &DL){
   LLVMContext &Ctx = LoadTy->getContext();
   uint64_t LoadSize = DL.getTypeSizeInBits(LoadTy)/8;
 
-  IRBuilder<> Builder(InsertPt->getParent(), InsertPt);
+  IRBuilder<> Builder(InsertPt);
 
   // We know that this method is only called when the mem transfer fully
   // provides the bits for the load.
   if (MemSetInst *MSI = dyn_cast<MemSetInst>(SrcInst)) {
     // memset(P, 'x', 1234) -> splat('x'), even if x is a variable, and
     // independently of what the offset is.
     Value *Val = MSI->getValue();
     if (LoadSize != 1)

test/Transforms/GVN/load-pre-nonlocal.ll

 for.end:
   %s.0.lcssa = phi i32 [ %add.lcssa, %for.cond.for.end_crit_edge ], [ 0, %entry ]
   ret i32 %s.0.lcssa
 }
 
 ; %1 is partially redundant if %0 can be widened to a 64-bit load.
 
 ; CHECK-LABEL: define i32 @overaligned_load
+; CHECK: if.then:
+; CHECK:   %0 = load i64
+; CHECK:   [[LSHR:%[0-9]+]] = lshr i64 %0, 32, !dbg [[LSHR_LOC:![0-9]+]]
+; CHECK:   trunc i64 [[LSHR]] to i32
 ; CHECK: if.end:
 ; CHECK-NOT: %1 = load i32, i32*
+; CHECK: [[LSHR_LOC]] = !DILocation(line: 101, column: 1, scope: !{{.*}})
 
 define i32 @overaligned_load(i32 %a, i32* nocapture %b) {
 entry:
-  %cmp = icmp sgt i32 %a, 0
-  br i1 %cmp, label %if.then, label %if.else
+  %cmp = icmp sgt i32 %a, 0, !dbg !14
+  br i1 %cmp, label %if.then, label %if.else, !dbg !14
 
 if.then:
-  %0 = load i32, i32* getelementptr inbounds (%struct.S1, %struct.S1* @s1, i64 0, i32 0), align 8, !tbaa !5
-  br label %if.end
+  %0 = load i32, i32* getelementptr inbounds (%struct.S1, %struct.S1* @s1, i64 0, i32 0), align 8, !tbaa !5, !dbg !15
+  br label %if.end, !dbg !15
 
 if.else:
-  %arrayidx = getelementptr inbounds i32, i32* %b, i64 2
-  store i32 10, i32* %arrayidx, align 4, !tbaa !5
-  br label %if.end
+  %arrayidx = getelementptr inbounds i32, i32* %b, i64 2, !dbg !16
+  store i32 10, i32* %arrayidx, align 4, !tbaa !5, !dbg !16
+  br label %if.end, !dbg !16
 
 if.end:
   %i.0 = phi i32 [ %0, %if.then ], [ 0, %if.else ]
   %p.0 = phi i32* [ getelementptr inbounds (%struct.S1, %struct.S1* @s1, i64 0, i32 0), %if.then ], [ %b, %if.else ]
-  %add.ptr = getelementptr inbounds i32, i32* %p.0, i64 1
-  %1 = load i32, i32* %add.ptr, align 4, !tbaa !5
-  %add1 = add nsw i32 %1, %i.0
-  ret i32 %add1
+  %add.ptr = getelementptr inbounds i32, i32* %p.0, i64 1, !dbg !17
+  %1 = load i32, i32* %add.ptr, align 4, !tbaa !5, !dbg !17
+  %add1 = add nsw i32 %1, %i.0, !dbg !17
+  ret i32 %add1, !dbg !17
 }
 
 !1 = !{!2, !2, i64 0}
 !2 = !{!"any pointer", !3, i64 0}
 !3 = !{!"omnipotent char", !4, i64 0}
 !4 = !{!"Simple C/C++ TBAA"}
 !5 = !{!6, !6, i64 0}
 !6 = !{!"int", !3, i64 0}
+
+!llvm.module.flags = !{!7, !8, !9}
+!7 = !{i32 2, !"Dwarf Version", i32 4}
+!8 = !{i32 2, !"Debug Info Version", i32 3}
+!9 = !{i32 1, !"PIC Level", i32 2}
+
+!10 = !{}
+!11 = !DISubroutineType(types: !10)
+!12 = !DIFile(filename: "test.cpp", directory: "/tmp")
+!13 = !DISubprogram(name: "test", scope: !12, file: !12, line: 99, type: !11, isLocal: false, isDefinition: true, scopeLine: 100, flags: DIFlagPrototyped, isOptimized: false, function: i32 (i32, i32*)* @overaligned_load, variables: !10)
+!14 = !DILocation(line: 100, column: 1, scope: !13)
+!15 = !DILocation(line: 101, column: 1, scope: !13)
+!16 = !DILocation(line: 102, column: 1, scope: !13)
+!17 = !DILocation(line: 103, column: 1, scope: !13)
+