[PATCH] D13685: [SCEV] Commute sign extends through nsw additions

[Sanjoy Das via llvm-commits]

sanjoy created this revision.
sanjoy added reviewers: atrick, hfinkel, reames, nlewycky.
sanjoy added a subscriber: llvm-commits.
sanjoy added a dependency: D13613: [SCEV] Mark AddExprs as nsw or nuw if legal.

Depends on D13613.

http://reviews.llvm.org/D13685

Files:
  lib/Analysis/ScalarEvolution.cpp
  test/Analysis/ScalarEvolution/no-wrap-add-exprs.ll

Index: test/Analysis/ScalarEvolution/no-wrap-add-exprs.ll
===================================================================
--- test/Analysis/ScalarEvolution/no-wrap-add-exprs.ll
+++ test/Analysis/ScalarEvolution/no-wrap-add-exprs.ll
@@ -42,3 +42,44 @@
 
   ret void
 }
+
+define void @f1(i8* %len_addr) {
+; CHECK-LABEL: Classifying expressions for: @f1
+ entry:
+  %len = load i8, i8* %len_addr, !range !0
+  %len_norange = load i8, i8* %len_addr
+; CHECK:  %len = load i8, i8* %len_addr, !range !0
+; CHECK-NEXT:  -->  %len U: [0,127) S: [0,127)
+; CHECK:  %len_norange = load i8, i8* %len_addr
+; CHECK-NEXT:  -->  %len_norange U: full-set S: full-set
+
+  %t0 = add i8 %len, -1
+  %t1 = add i8 %len, -2
+; CHECK:  %t0 = add i8 %len, -1
+; CHECK-NEXT:  -->  (-1 + %len)<nsw> U: [-1,126) S: [-1,126)
+; CHECK:  %t1 = add i8 %len, -2
+; CHECK-NEXT:  -->  (-2 + %len)<nsw> U: [-2,125) S: [-2,125)
+
+  %t0.sext = sext i8 %t0 to i16
+  %t1.sext = sext i8 %t1 to i16
+; CHECK:  %t0.sext = sext i8 %t0 to i16
+; CHECK-NEXT:  -->  (-1 + (zext i8 %len to i16))<nsw> U: [-1,126) S: [-1,126)
+; CHECK:  %t1.sext = sext i8 %t1 to i16
+; CHECK-NEXT:  -->  (-2 + (zext i8 %len to i16))<nsw> U: [-2,125) S: [-2,125)
+
+  %q0 = add i8 %len_norange, 1
+  %q1 = add i8 %len_norange, 2
+; CHECK:  %q0 = add i8 %len_norange, 1
+; CHECK-NEXT:  -->  (1 + %len_norange) U: full-set S: full-set
+; CHECK:  %q1 = add i8 %len_norange, 2
+; CHECK-NEXT:  -->  (2 + %len_norange) U: full-set S: full-set
+
+  %q0.sext = sext i8 %q0 to i16
+  %q1.sext = sext i8 %q1 to i16
+; CHECK:  %q0.sext = sext i8 %q0 to i16
+; CHECK-NEXT:  -->  (sext i8 (1 + %len_norange) to i16) U: [-128,128) S: [-128,128)
+; CHECK:  %q1.sext = sext i8 %q1 to i16
+; CHECK-NEXT:  -->  (sext i8 (2 + %len_norange) to i16) U: [-128,128) S: [-128,128)
+
+  ret void
+}
Index: lib/Analysis/ScalarEvolution.cpp
===================================================================
--- lib/Analysis/ScalarEvolution.cpp
+++ lib/Analysis/ScalarEvolution.cpp
@@ -1631,6 +1631,15 @@
         }
       }
     }
+
+    if (SA->getNoWrapFlags(SCEV::FlagNSW)) {
+      // If the addition does not sign overflow then we can, by definition,
+      // commute the sign extension with the addition operation.
+      SmallVector<const SCEV *, 4> Ops;
+      for (const auto *Op : SA->operands())
+        Ops.push_back(getSignExtendExpr(Op, Ty));
+      return getAddExpr(Ops, SCEV::FlagNSW);
+    }
   }
   // If the input value is a chrec scev, and we can prove that the value
   // did not overflow the old, smaller, value, we can sign extend all of the


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