Add some shortcuts in LazyValueInfo to reduce compile time of Correlated Value Propagation.

The patch is to partially fix PR10584. Correlated Value Propagation queries LVI
to check non-null for pointer params of each callsite. If we know the def of
param is an alloca instruction, we know it is non-null and can return early from
LVI. Similarly, CVP queries LVI to check whether pointer for each mem access is
constant. If the def of the pointer is an alloca instruction, we know it is not
a constant pointer. These shortcuts can reduce the cost of CVP significantly.

Differential Revision: https://reviews.llvm.org/D18066

llvm-svn: 281586

1 files changed, 48 insertions, 0 deletions

diff --git a/llvm/test/Transforms/CorrelatedValuePropagation/alloca.ll b/llvm/test/Transforms/CorrelatedValuePropagation/alloca.ll
new file mode 100644
index 00000000000..2ae1664fdee
--- /dev/null
+++ b/llvm/test/Transforms/CorrelatedValuePropagation/alloca.ll
@@ -0,0 +1,48 @@
+; RUN: opt -S -correlated-propagation -debug-only=lazy-value-info <%s 2>&1 | FileCheck %s
+;
+; Shortcut in Correlated Value Propagation ensures not to take Lazy Value Info
+; analysis for %a.i and %tmp because %a.i is defined by alloca and %tmp is
+; defined by alloca + bitcast. We know the ret value of alloca is nonnull.
+;
+; CHECK-NOT: LVI Getting edge value   %a.i = alloca i64, align 8 at 'for.body'
+; CHECK-NOT: LVI Getting edge value   %tmp = bitcast i64* %a.i to i8* from 'for.cond' to 'for.body'
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+@.str = private unnamed_addr constant [8 x i8] c"a = %l\0A\00", align 1
+
+; Function Attrs: argmemonly nounwind
+declare void @llvm.lifetime.start(i64, i8* nocapture)
+
+declare void @hoo(i64*)
+
+declare i32 @printf(i8* nocapture readonly, ...)
+
+; Function Attrs: argmemonly nounwind
+declare void @llvm.lifetime.end(i64, i8* nocapture)
+
+define void @goo(i32 %N, i64* %b) {
+entry:
+  %a.i = alloca i64, align 8
+  %tmp = bitcast i64* %a.i to i8*
+  %c = getelementptr inbounds i64, i64* %b, i64 0
+  br label %for.cond
+
+for.cond:                                         ; preds = %for.body, %entry
+  %i.0 = phi i32 [ 0, %entry ], [ %inc, %for.body ]
+  %cmp = icmp slt i32 %i.0, %N
+  br i1 %cmp, label %for.body, label %for.end
+
+for.body:                                         ; preds = %for.cond
+  call void @llvm.lifetime.start(i64 8, i8* %tmp)
+  call void @hoo(i64* %a.i)
+  call void @hoo(i64* %c)
+  %tmp1 = load volatile i64, i64* %a.i, align 8
+  %call.i = call i32 (i8*, ...) @printf(i8* getelementptr inbounds ([8 x i8], [8 x i8]* @.str, i64 0, i64 0), i64 %tmp1)
+  call void @llvm.lifetime.end(i64 8, i8* %tmp)
+  %inc = add nsw i32 %i.0, 1
+  br label %for.cond
+
+for.end:                                          ; preds = %for.cond
+  ret void
+}