[SCEVExpander] Make findExistingExpansion smarter

Summary:
Extending findExistingExpansion can use existing value in ExprValueMap.
This patch gives 0.3~0.5% performance improvements on 
benchmarks(test-suite, spec2000, spec2006, commercial benchmark)
   
Reviewers: mzolotukhin, sanjoy, zzheng

Differential Revision: http://reviews.llvm.org/D15559

llvm-svn: 260938

1 files changed, 34 insertions, 0 deletions

diff --git a/llvm/test/Transforms/LoopUnroll/high-cost-trip-count-computation.ll b/llvm/test/Transforms/LoopUnroll/high-cost-trip-count-computation.ll
index 6b1943f13ba..b4f7565c395 100644
--- a/llvm/test/Transforms/LoopUnroll/high-cost-trip-count-computation.ll
+++ b/llvm/test/Transforms/LoopUnroll/high-cost-trip-count-computation.ll
@@ -24,4 +24,38 @@ loopexit:                             ; preds = %loop
   ret i32 0
 }
 
+;; Though SCEV for loop tripcount contains division,
+;; it shouldn't be considered expensive, since the division already
+;; exists in the code and we don't need to expand it once more.
+;; Thus, it shouldn't prevent us from unrolling the loop.
+
+define i32 @test2(i64* %loc, i64 %conv7) {
+; CHECK-LABEL: @test2(
+; CHECK: udiv
+; CHECK: udiv
+; CHECK-NOT: udiv
+; CHECK-LABEL: for.body.prol
+entry:
+  %rem0 = load i64, i64* %loc, align 8
+  %ExpensiveComputation = udiv i64 %rem0, 42 ; <<< Extra computations are added to the trip-count expression
+  br label %bb1
+bb1:
+  %div11 = udiv i64 %ExpensiveComputation, %conv7
+  %cmp.i38 = icmp ugt i64 %div11, 1
+  %div12 = select i1 %cmp.i38, i64 %div11, i64 1
+  br label %for.body
+for.body:
+  %rem1 = phi i64 [ %rem0, %bb1 ], [ %rem2, %for.body ]
+  %k1 = phi i64 [ %div12, %bb1 ], [ %dec, %for.body ]
+  %mul1 = mul i64 %rem1, 48271
+  %rem2 = urem i64 %mul1, 2147483647
+  %dec = add i64 %k1, -1
+  %cmp = icmp eq i64 %dec, 0
+  br i1 %cmp, label %exit, label %for.body
+exit:
+  %rem3 = phi i64 [ %rem2, %for.body ]
+  store i64 %rem3, i64* %loc, align 8
+  ret i32 0
+}
+
 !0 = !{i64 1, i64 100}