Use value ranges to fold ext(trunc) in SCEV when possible.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@124062 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 68 insertions, 0 deletions

diff --git a/lib/Analysis/ScalarEvolution.cpp b/lib/Analysis/ScalarEvolution.cpp
index 63602ff..0f2afb2 100644
--- a/lib/Analysis/ScalarEvolution.cpp
+++ b/lib/Analysis/ScalarEvolution.cpp
@@ -898,6 +898,23 @@ const SCEV *ScalarEvolution::getZeroExtendExpr(const SCEV *Op,
   void *IP = 0;
   if (const SCEV *S = UniqueSCEVs.FindNodeOrInsertPos(ID, IP)) return S;
 
+  // zext(trunc(x)) --> zext(x) or x or trunc(x)
+  if (const SCEVTruncateExpr *ST = dyn_cast<SCEVTruncateExpr>(Op)) {
+    // It's possible the bits taken off by the truncate were all zero bits. If
+    // so, we should be able to simplify this further.
+    const SCEV *X = ST->getOperand();
+    ConstantRange CR = getUnsignedRange(X);
+    unsigned OrigBits = CR.getBitWidth();
+    unsigned TruncBits = getTypeSizeInBits(ST->getType());
+    unsigned NewBits = getTypeSizeInBits(Ty);
+    if (CR.truncate(TruncBits).zeroExtend(NewBits).contains(
+            CR.zextOrTrunc(NewBits))) {
+      if (NewBits > OrigBits) return getZeroExtendExpr(X, Ty);
+      if (NewBits < OrigBits) return getTruncateExpr(X, Ty);
+      return X;
+    }
+  }
+
   // If the input value is a chrec scev, and we can prove that the value
   // did not overflow the old, smaller, value, we can zero extend all of the
   // operands (often constants).  This allows analysis of something like
@@ -1039,6 +1056,23 @@ const SCEV *ScalarEvolution::getSignExtendExpr(const SCEV *Op,
   if (isKnownNonNegative(Op))
     return getZeroExtendExpr(Op, Ty);
 
+  // sext(trunc(x)) --> sext(x) or x or trunc(x)
+  if (const SCEVTruncateExpr *ST = dyn_cast<SCEVTruncateExpr>(Op)) {
+    // It's possible the bits taken off by the truncate were all sign bits. If
+    // so, we should be able to simplify this further.
+    const SCEV *X = ST->getOperand();
+    ConstantRange CR = getSignedRange(X);
+    unsigned OrigBits = CR.getBitWidth();
+    unsigned TruncBits = getTypeSizeInBits(ST->getType());
+    unsigned NewBits = getTypeSizeInBits(Ty);
+    if (CR.truncate(TruncBits).signExtend(NewBits).contains(
+            CR.sextOrTrunc(NewBits))) {
+      if (NewBits > OrigBits) return getSignExtendExpr(X, Ty);
+      if (NewBits < OrigBits) return getTruncateExpr(X, Ty);
+      return X;
+    }
+  }
+
   // 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
   // operands (often constants).  This allows analysis of something like
diff --git a/test/Analysis/ScalarEvolution/fold.ll b/test/Analysis/ScalarEvolution/fold.ll
index 3c1b6ae..90012a3 100644
--- a/test/Analysis/ScalarEvolution/fold.ll
+++ b/test/Analysis/ScalarEvolution/fold.ll
@@ -22,3 +22,37 @@ define i8 @test3(i8 %x) {
 ; CHECK: (3 * %x)
   ret i8 %C
 }
+
+define void @test4(i32 %x) {
+entry:
+  %0 = icmp sge i32 %x, 0
+  br i1 %0, label %loop, label %exit
+loop:
+  %A = phi i32 [0, %entry], [%I, %loop]
+  %rand = icmp sgt i32 %A, 10
+  %Z = select i1 %rand, i32 %A, i32 10
+  %B = trunc i32 %Z to i16
+  %C = sext i16 %B to i30
+; CHECK: %C =
+; CHECK-NEXT: (trunc i32 (10 smax {0,+,1}<%loop>) to i30)
+  %D = sext i16 %B to i32
+; CHECK: %D =
+; CHECK-NEXT: (10 smax {0,+,1}<%loop>)
+  %E = sext i16 %B to i34
+; CHECK: %E =
+; CHECK-NEXT: (zext i32 (10 smax {0,+,1}<%loop>) to i34)
+  %F = zext i16 %B to i30
+; CHECK: %F =
+; CHECK-NEXT: (trunc i32 (10 smax {0,+,1}<%loop>) to i30
+  %G = zext i16 %B to i32
+; CHECK: %G =
+; CHECK-NEXT: (10 smax {0,+,1}<%loop>)
+  %H = zext i16 %B to i34
+; CHECK: %H =
+; CHECK-NEXT: (zext i32 (10 smax {0,+,1}<%loop>) to i34)
+  %I = add i32 %A, 1
+  %1 = icmp ne i32 %A, 20
+  br i1 %1, label %loop, label %exit
+exit:
+  ret void
+}
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