[polly] Add diagnostic remark for ReportVariantBasePtr

[Tobias Grosser]

On 26/06/2014 22:59, David Blaikie wrote:
> The current state is that just using -R should do the right thing
> (include column info everywhere), but using it combined with any -g
> will omit column info unless you request it explicitly
> (-gcolumn-info).
>
> We're talking on llvm-dev about turning on column info by default so
> that -R + -g results in the same diagnostic quality as -R alone.

Sorry, the latest messages in this thread are inspired be the llvm-dev 
discussion. However, it seems that even with -gcolumn-info the loads and 
stores in the test case below have the same column info. My 
understanding is that clang even with -gcolumn-info does not create
this information for each subexpression, right? Would you expect 
different column info for the load and store instructions?

Here the test case:

  struct b {
    double **b;
  };

  void a(struct b *A, int p) {
    for (int i=0; i<32; i++)
      A->b[i] = A->b[i+p];   << -- Here
  }

here the output of 'clang -c  -O3  -Rpass-missed=polly -S -emit-llvm'

   %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next.1, %for.body ]
   %1 = add nsw i64 %indvars.iv, %0, !dbg !2
   %2 = load double*** %b, align 8, !dbg !2, !tbaa !10
   %arrayidx = getelementptr inbounds double** %2, i64 %1, !dbg !2
   %3 = load double** %arrayidx, align 8, !dbg !2, !tbaa !15
   %arrayidx3 = getelementptr inbounds double** %2, i64 %indvars.iv, !dbg !2
   store double* %3, double** %arrayidx3, align 8, !dbg !2, !tbaa !15
   %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1, !dbg !9
   %4 = add nsw i64 %indvars.iv.next, %0, !dbg !2
   %5 = load double*** %b, align 8, !dbg !2, !tbaa !10
   %arrayidx.1 = getelementptr inbounds double** %5, i64 %4, !dbg !2
   %6 = load double** %arrayidx.1, align 8, !dbg !2, !tbaa !15
   %arrayidx3.1 = getelementptr inbounds double** %5, i64 
%indvars.iv.next, !dbg !2
   store double* %6, double** %arrayidx3.1, align 8, !dbg !2, !tbaa !15
   %indvars.iv.next.1 = add nuw nsw i64 %indvars.iv.next, 1, !dbg !9
   %exitcond.1 = icmp eq i64 %indvars.iv.next.1, 32, !dbg !9
   br i1 %exitcond.1, label %for.end, label %for.body, !dbg !9

all loads/stores have !dbg2

With this clang hack:

index 62ecc73..53c63f4 100644
--- a/lib/CodeGen/CGExpr.cpp
+++ b/lib/CodeGen/CGExpr.cpp
@@ -771,6 +771,9 @@ LValue CodeGenFunction::EmitCheckedLValue(const Expr 
*E, TypeCheckKind TCK) {
  /// length type, this is not possible.
  ///
  LValue CodeGenFunction::EmitLValue(const Expr *E) {
+  if (CGDebugInfo *DI = getDebugInfo()) {
+  DI->EmitLocation(Builder, E->getLocEnd(), true);
+  }
    switch (E->getStmtClass()) {
    default: return EmitUnsupportedLValue(E, "l-value expression");

We get:
   %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next.1, %for.body ]
   %1 = add nsw i64 %indvars.iv, %0, !dbg !10
   %2 = load double*** %b, align 8, !dbg !2, !tbaa !11
   %arrayidx = getelementptr inbounds double** %2, i64 %1, !dbg !2
   %3 = load double** %arrayidx, align 8, !dbg !2, !tbaa !16
   %arrayidx3 = getelementptr inbounds double** %2, i64 %indvars.iv, 
!dbg !17
   store double* %3, double** %arrayidx3, align 8, !dbg !17, !tbaa !16
   %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1, !dbg !9
   %4 = add nsw i64 %indvars.iv.next, %0, !dbg !10
   %5 = load double*** %b, align 8, !dbg !2, !tbaa !11
   %arrayidx.1 = getelementptr inbounds double** %5, i64 %4, !dbg !2
   %6 = load double** %arrayidx.1, align 8, !dbg !2, !tbaa !16
   %arrayidx3.1 = getelementptr inbounds double** %5, i64 
%indvars.iv.next, !dbg !17
   store double* %6, double** %arrayidx3.1, align 8, !dbg !17, !tbaa !16
   %indvars.iv.next.1 = add nuw nsw i64 %indvars.iv.next, 1, !dbg !9
   %exitcond.1 = icmp eq i64 %indvars.iv.next.1, 32, !dbg !9
   br i1 %exitcond.1, label %for.end, label %for.body, !dbg !9

Now the store has !dbg !17 and the loads have !dbg !2

This is enough for Polly reference individual errors with column carets 
(which was not working without the patch):

/tmp/test.c:7:16: remark: The base address of this array is not 
invariant inside the loop [-Rpass-missed=polly-detect]
      A->b[i] = A->b[i+p];
                ^
/tmp/test.c:7:6: remark: The base address of this array is not invariant 
inside the loop [-Rpass-missed=polly-detect]
      A->b[i] = A->b[i+p];
      ^

I have no idea on which granularity clang is expected to provide column 
info. Has anybody an idea? Should clang emit column info for individual 
load instructions?

Cheers,
Tobias