[SimplifyIndVar] Constant fold IV users

This patch tries to transform cases like:

for (unsigned i = 0; i < N; i += 2) {
  bool c0 = (i & 0x1) == 0;
  bool c1 = ((i + 1) & 0x1) == 1;
}
To

for (unsigned i = 0; i < N; i += 2) {
  bool c0 = true;
  bool c1 = true;
}

This commit also update test/Transforms/IndVarSimplify/replace-srem-by-urem.ll to prevent constant folding.

Differential Revision: https://reviews.llvm.org/D38272

llvm-svn: 314266

2 files changed, 48 insertions, 1 deletions

diff --git a/llvm/test/Transforms/IndVarSimplify/constant-fold.ll b/llvm/test/Transforms/IndVarSimplify/constant-fold.ll
new file mode 100644
index 00000000000..a35349aa1f5
--- /dev/null
+++ b/llvm/test/Transforms/IndVarSimplify/constant-fold.ll
@@ -0,0 +1,47 @@
+; RUN: opt -indvars -S < %s | FileCheck %s
+
+define void @test0(i32* %x) {
+entry:
+  br label %for.inc
+
+for.inc:                                          ; preds = %for.inc, %entry
+  %i.01 = phi i32 [ 0, %entry ], [ %add, %for.inc ]
+  %and = and i32 %i.01, 3
+  %cmp1 = icmp eq i32 %and, 0
+  %cond = select i1 %cmp1, i32 0, i32 1
+  store i32 %cond, i32* %x, align 4
+  %add = add i32 %i.01, 4
+  %cmp = icmp ult i32 %add, 8
+  br i1 %cmp, label %for.inc, label %for.end
+
+for.end:                                          ; preds = %for.inc
+  ret void
+}
+
+; Should fold the condition of the select into constant
+; CHECK-LABEL: void @test
+; CHECK:         icmp eq i32 0, 0
+
+define void @test1(i32* %a) {
+entry:
+  br label %for.body
+
+for.body:                                         ; preds = %entry, %for.body
+  %i.01 = phi i32 [ 0, %entry ], [ %inc, %for.body ]
+  %mul = mul nsw i32 %i.01, 64
+  %rem = srem i32 %mul, 8
+  %idxprom = sext i32 %rem to i64
+  %arrayidx = getelementptr inbounds i32, i32* %a, i64 %idxprom
+  store i32 %i.01, i32* %arrayidx, align 4
+  %inc = add nsw i32 %i.01, 1
+  %cmp = icmp slt i32 %inc, 64
+  br i1 %cmp, label %for.body, label %for.end
+
+for.end:                                          ; preds = %for.body
+  ret void
+}
+
+; Should fold the rem since %mul is multiple of 8
+; CHECK-LABEL: @test1(
+; CHECK-NOT:     rem
+; CHECK:         sext i32 0 to i64
diff --git a/llvm/test/Transforms/IndVarSimplify/replace-srem-by-urem.ll b/llvm/test/Transforms/IndVarSimplify/replace-srem-by-urem.ll
index 6629420df55..ec1ccffbc5c 100644
--- a/llvm/test/Transforms/IndVarSimplify/replace-srem-by-urem.ll
+++ b/llvm/test/Transforms/IndVarSimplify/replace-srem-by-urem.ll
@@ -71,7 +71,7 @@ entry:
 for.body:                                         ; preds = %entry, %for.body
   %i.01 = phi i32 [ 0, %entry ], [ %inc, %for.body ]
   %mul = mul nsw i32 %i.01, 64
-  %rem = srem i32 %mul, 8
+  %rem = srem i32 %mul, 7
 ; CHECK:     urem
 ; CHECK-NOT: srem
   %idxprom = sext i32 %rem to i64