Update loop unroller cost model to make sure debug info does not affect optimization decisions.

[danielcdh]

Summary

Debug info should *not* affect optimization decisions. This patch updates loop unroller cost model to make it not affected by debug info.

[mzolotukhin]

LGTM!

lib/Transforms/Scalar/LoopUnrollPass.cpp

for (unsigned Iteration = 0; Iteration < TripCount; ++Iteration) {
     // Note that we *must not* cache the size, this loop grows the worklist.
     for (unsigned Idx = 0; Idx != BBWorklist.size(); ++Idx) {
       BasicBlock *BB = BBWorklist[Idx];
 
       // Visit all instructions in the given basic block and try to simplify
       // it.  We don't change the actual IR, just count optimization
       // opportunities.
       for (Instruction &I : *BB) {
+        if (isa<DbgInfoIntrinsic>(I))
+          continue;
+
         // Track this instruction's expected baseline cost when executing the
         // rolled loop form.
         RolledDynamicCost += TTI.getUserCost(&I);
 
         // Visit the instruction to analyze its loop cost after unrolling,
         // and if the visitor returns true, mark the instruction as free after
         // unrolling and continue.
         bool IsFree = Analyzer.visit(I);

test/Transforms/LoopUnroll/unroll-pragmas.ll

-; RUN: opt < %s -loop-unroll -pragma-unroll-threshold=1024 -S | FileCheck %s
-; RUN: opt < %s -loop-unroll -loop-unroll -pragma-unroll-threshold=1024 -S | FileCheck %s
+; RUN: opt < %s -loop-unroll -pragma-unroll-threshold=1024 -unroll-max-iteration-count-to-analyze=40 -S | FileCheck %s
+; RUN: opt < %s -loop-unroll -loop-unroll -pragma-unroll-threshold=1024 -unroll-max-iteration-count-to-analyze=40 -S | FileCheck %s
 ;
 ; Run loop unrolling twice to verify that loop unrolling metadata is properly
 ; removed and further unrolling is disabled after the pass is run once.
 
 target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-unknown-linux-gnu"
 
 ; loop4 contains a small loop which should be completely unrolled by
for.body:                                         ; preds = %for.body, %entry
   %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
   %exitcond = icmp eq i64 %indvars.iv.next, 4
   br i1 %exitcond, label %for.end, label %for.body
 
 for.end:                                          ; preds = %for.body
   ret void
 }
 
+; loop4_with_dbg contains a small loop which should be completely unrolled by
+; the default unrolling heuristics. There is DbgInfoIntrinsic inside the loop
+; body, which should not block unrolling.
+;
+; CHECK-LABEL: @loop4_dbg(
+; CHECK-NOT: br i1
+define void @loop4_dbg(i32* nocapture %a) {
+entry:
+  br label %for.body
+
+for.body:                                         ; preds = %for.body, %entry
+  %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
+  %arrayidx = getelementptr inbounds i32, i32* %a, i64 %indvars.iv
+  %0 = load i32, i32* %arrayidx, align 4
+  call void @llvm.dbg.value(metadata i32 0, i64 0, metadata !22, metadata !DIExpression()), !dbg !24
+  %inc = add nsw i32 %0, 1
+  store i32 %inc, i32* %arrayidx, align 4
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+  %exitcond = icmp eq i64 %indvars.iv.next, 40
+  br i1 %exitcond, label %for.end, label %for.body
+
+for.end:                                          ; preds = %for.body
+  ret void
+}
+
 ; #pragma clang loop unroll(disable)
 ;
 ; CHECK-LABEL: @loop4_with_disable(
 ; CHECK: store i32
 ; CHECK-NOT: store i32
 ; CHECK: br i1
 define void @loop4_with_disable(i32* nocapture %a) {
 entry:
for.body:                                         ; preds = %entry, %for.body
   %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
   %lftr.wideiv = trunc i64 %indvars.iv.next to i32
   %exitcond = icmp eq i32 %lftr.wideiv, %b
   br i1 %exitcond, label %for.end, label %for.body, !llvm.loop !16
 
 for.end:                                          ; preds = %for.body, %entry
   ret void
 }
+
+declare void @llvm.dbg.value(metadata, i64, metadata, metadata)
+
+!llvm.module.flags = !{!18, !19}
+!llvm.dbg.cu = !{!20}
+
 !16 = !{!16, !17}
 !17 = !{!"llvm.loop.unroll.count", i32 3}
+!18 = !{i32 2, !"Dwarf Version", i32 4}
+!19 = !{i32 2, !"Debug Info Version", i32 3}
+!20 = distinct !DICompileUnit(language: DW_LANG_C99, file: !23)
+!21 = distinct !DISubprogram(name: "foo", unit: !20)
+!22 = !DILocalVariable(name: "b", line: 1, arg: 2, scope: !21)
+!23 = !DIFile(filename: "a.c", directory: "a/b")
+!24 = !DILocation(line: 1, column: 14, scope: !21)