This patch teaches IndVarSimplify to add nuw and nsw to certain kinds

of operations that provably don't overflow. For example, we can prove
%civ.inc below does not sign-overflow. With this change,
IndVarSimplify changes %civ.inc to an add nsw.

  define i32 @foo(i32* %array, i32* %length_ptr, i32 %init) {
   entry:
    %length = load i32* %length_ptr, !range !0
    %len.sub.1 = sub i32 %length, 1
    %upper = icmp slt i32 %init, %len.sub.1
    br i1 %upper, label %loop, label %exit
  
   loop:
    %civ = phi i32 [ %init, %entry ], [ %civ.inc, %latch ]
    %civ.inc = add i32 %civ, 1
    %cmp = icmp slt i32 %civ.inc, %length
    br i1 %cmp, label %latch, label %break
  
   latch:
    store i32 0, i32* %array
    %check = icmp slt i32 %civ.inc, %len.sub.1
    br i1 %check, label %loop, label %break
  
   break:
    ret i32 %civ.inc
  
   exit:
    ret i32 42
  }

Differential Revision: http://reviews.llvm.org/D6748

llvm-svn: 225282

1 files changed, 214 insertions, 0 deletions

diff --git a/llvm/test/Transforms/IndVarSimplify/strengthen-overflow.ll b/llvm/test/Transforms/IndVarSimplify/strengthen-overflow.ll
new file mode 100644
index 00000000000..07e489e0338
--- /dev/null
+++ b/llvm/test/Transforms/IndVarSimplify/strengthen-overflow.ll
@@ -0,0 +1,214 @@
+; RUN: opt < %s -indvars -S | FileCheck %s
+
+define i32 @test.signed.add.0(i32* %array, i32 %length, i32 %init) {
+; CHECK-LABEL: @test.signed.add.0
+ entry:
+  %upper = icmp slt i32 %init, %length
+  br i1 %upper, label %loop, label %exit
+
+ loop:
+; CHECK-LABEL: loop
+  %civ = phi i32 [ %init, %entry ], [ %civ.inc, %latch ]
+  %civ.inc = add i32 %civ, 1
+; CHECK: %civ.inc = add nsw i32 %civ, 1
+  %cmp = icmp slt i32 %civ.inc, %length
+  br i1 %cmp, label %latch, label %break
+
+ latch:
+  store i32 0, i32* %array
+  %check = icmp slt i32 %civ.inc, %length
+  br i1 %check, label %loop, label %break
+
+ break:
+  ret i32 %civ.inc
+
+ exit:
+  ret i32 42
+}
+
+define i32 @test.signed.add.1(i32* %array, i32 %length, i32 %init) {
+; CHECK-LABEL: @test.signed.add.1
+ entry:
+  %upper = icmp sle i32 %init, %length
+  br i1 %upper, label %loop, label %exit
+
+ loop:
+; CHECK-LABEL: loop
+  %civ = phi i32 [ %init, %entry ], [ %civ.inc, %latch ]
+  %civ.inc = add i32 %civ, 1
+; CHECK: %civ.inc = add i32 %civ, 1
+  %cmp = icmp slt i32 %civ.inc, %length
+  br i1 %cmp, label %latch, label %break
+
+ latch:
+  store i32 0, i32* %array
+  %check = icmp slt i32 %civ.inc, %length
+  br i1 %check, label %loop, label %break
+
+ break:
+  ret i32 %civ.inc
+
+ exit:
+  ret i32 42
+}
+
+define i32 @test.signed.sub.0(i32* %array, i32 %length, i32 %init) {
+; CHECK-LABEL: @test.signed.sub.0
+ entry:
+  %upper = icmp sgt i32 %init, %length
+  br i1 %upper, label %loop, label %exit
+
+ loop:
+; CHECK-LABEL: loop
+  %civ = phi i32 [ %init, %entry ], [ %civ.inc, %latch ]
+  %civ.inc = sub i32 %civ, 1
+; CHECK: %civ.inc = sub nsw i32 %civ, 1
+  %cmp = icmp slt i32 %civ.inc, %length
+  br i1 %cmp, label %latch, label %break
+
+ latch:
+  store i32 0, i32* %array
+  %check = icmp sgt i32 %civ.inc, %length
+  br i1 %check, label %loop, label %break
+
+ break:
+  ret i32 %civ.inc
+
+ exit:
+  ret i32 42
+}
+
+define i32 @test.signed.sub.1(i32* %array, i32 %length, i32 %init) {
+; CHECK-LABEL: @test.signed.sub.1
+ entry:
+  %upper = icmp sgt i32 %init, %length
+  br i1 %upper, label %loop, label %exit
+
+ loop:
+; CHECK-LABEL: loop
+  %civ = phi i32 [ %init, %entry ], [ %civ.inc, %latch ]
+  %civ.inc = sub i32 %civ, 1
+; CHECK: %civ.inc = sub i32 %civ, 1
+  %cmp = icmp slt i32 %civ.inc, %length
+  br i1 %cmp, label %latch, label %break
+
+ latch:
+  store i32 0, i32* %array
+  %check = icmp sge i32 %civ.inc, %length
+  br i1 %check, label %loop, label %break
+
+ break:
+  ret i32 %civ.inc
+
+ exit:
+  ret i32 42
+}
+
+define i32 @test.unsigned.add.0(i32* %array, i32 %length, i32 %init) {
+; CHECK-LABEL: @test.unsigned.add.0
+ entry:
+  %upper = icmp ult i32 %init, %length
+  br i1 %upper, label %loop, label %exit
+
+ loop:
+; CHECK-LABEL: loop
+  %civ = phi i32 [ %init, %entry ], [ %civ.inc, %latch ]
+  %civ.inc = add i32 %civ, 1
+; CHECK: %civ.inc = add nuw i32 %civ, 1
+  %cmp = icmp slt i32 %civ.inc, %length
+  br i1 %cmp, label %latch, label %break
+
+ latch:
+  store i32 0, i32* %array
+  %check = icmp ult i32 %civ.inc, %length
+  br i1 %check, label %loop, label %break
+
+ break:
+  ret i32 %civ.inc
+
+ exit:
+  ret i32 42
+}
+
+define i32 @test.unsigned.add.1(i32* %array, i32 %length, i32 %init) {
+; CHECK-LABEL: @test.unsigned.add.1
+ entry:
+  %upper = icmp ule i32 %init, %length
+  br i1 %upper, label %loop, label %exit
+
+ loop:
+; CHECK-LABEL: loop
+  %civ = phi i32 [ %init, %entry ], [ %civ.inc, %latch ]
+  %civ.inc = add i32 %civ, 1
+; CHECK: %civ.inc = add i32 %civ, 1
+  %cmp = icmp slt i32 %civ.inc, %length
+  br i1 %cmp, label %latch, label %break
+
+ latch:
+  store i32 0, i32* %array
+  %check = icmp ult i32 %civ.inc, %length
+  br i1 %check, label %loop, label %break
+
+ break:
+  ret i32 %civ.inc
+
+ exit:
+  ret i32 42
+}
+
+define i32 @test.unsigned.sub.0(i32* %array, i32* %length_ptr, i32 %init) {
+; CHECK-LABEL: @test.unsigned.sub.0
+ entry:
+  %length = load i32* %length_ptr, !range !0
+  %upper = icmp ult i32 %init, %length
+  br i1 %upper, label %loop, label %exit
+
+ loop:
+; CHECK-LABEL: loop
+  %civ = phi i32 [ %init, %entry ], [ %civ.inc, %latch ]
+  %civ.inc = sub i32 %civ, 2
+; CHECK: %civ.inc = sub nuw i32 %civ, 2
+  %cmp = icmp slt i32 %civ.inc, %length
+  br i1 %cmp, label %latch, label %break
+
+ latch:
+  store i32 0, i32* %array
+  %check = icmp ult i32 %civ.inc, %length
+  br i1 %check, label %loop, label %break
+
+ break:
+  ret i32 %civ.inc
+
+ exit:
+  ret i32 42
+}
+
+define i32 @test.unsigned.sub.1(i32* %array, i32* %length_ptr, i32 %init) {
+; CHECK-LABEL: @test.unsigned.sub.1
+ entry:
+  %length = load i32* %length_ptr, !range !1
+  %upper = icmp ult i32 %init, %length
+  br i1 %upper, label %loop, label %exit
+
+ loop:
+; CHECK-LABEL: loop
+  %civ = phi i32 [ %init, %entry ], [ %civ.inc, %latch ]
+  %civ.inc = sub i32 %civ, 2
+; CHECK: %civ.inc = sub i32 %civ, 2
+  %cmp = icmp slt i32 %civ.inc, %length
+  br i1 %cmp, label %latch, label %break
+
+ latch:
+  store i32 0, i32* %array
+  %check = icmp ult i32 %civ.inc, %length
+  br i1 %check, label %loop, label %break
+
+ break:
+  ret i32 %civ.inc
+
+ exit:
+  ret i32 42
+}
+
+!0 = !{i32 0, i32 2}
+!1 = !{i32 0, i32 42}