[PATCH] D97170: [ValueTracking] Improve ComputeNumSignBits for SRem.

[Craig Topper via Phabricator via llvm-commits]

craig.topper updated this revision to Diff 325481.
craig.topper added a comment.

Rebase


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D97170/new/

https://reviews.llvm.org/D97170

Files:
  llvm/lib/Analysis/ValueTracking.cpp
  llvm/test/Transforms/InstCombine/with_overflow.ll


Index: llvm/test/Transforms/InstCombine/with_overflow.ll
===================================================================
--- llvm/test/Transforms/InstCombine/with_overflow.ll
+++ llvm/test/Transforms/InstCombine/with_overflow.ll
@@ -332,11 +332,7 @@
 
 define i1 @overflow_mod_mul2(i16 %v1, i32 %v2) nounwind {
 ; CHECK-LABEL: @overflow_mod_mul2(
-; CHECK-NEXT:    [[A:%.*]] = sext i16 [[V1:%.*]] to i32
-; CHECK-NEXT:    [[REM:%.*]] = srem i32 [[A]], [[V2:%.*]]
-; CHECK-NEXT:    [[T:%.*]] = call { i32, i1 } @llvm.smul.with.overflow.i32(i32 [[REM]], i32 [[REM]])
-; CHECK-NEXT:    [[OBIT:%.*]] = extractvalue { i32, i1 } [[T]], 1
-; CHECK-NEXT:    ret i1 [[OBIT]]
+; CHECK-NEXT:    ret i1 false
 ;
   %a = sext i16 %v1 to i32
   %rem = srem i32 %a, %v2
Index: llvm/lib/Analysis/ValueTracking.cpp
===================================================================
--- llvm/lib/Analysis/ValueTracking.cpp
+++ llvm/lib/Analysis/ValueTracking.cpp
@@ -2784,6 +2784,8 @@
     }
 
     case Instruction::SRem: {
+      Tmp = ComputeNumSignBits(U->getOperand(0), Depth + 1, Q);
+
       const APInt *Denominator;
       // srem X, C -> we know that the result is within [-C+1,C) when C is a
       // positive constant.  This let us put a lower bound on the number of sign
@@ -2791,30 +2793,25 @@
       if (match(U->getOperand(1), m_APInt(Denominator))) {
 
         // Ignore non-positive denominator.
-        if (!Denominator->isStrictlyPositive())
-          break;
-
-        // Calculate the incoming numerator bits. SRem by a positive constant
-        // can't lower the number of sign bits.
-        unsigned NumrBits = ComputeNumSignBits(U->getOperand(0), Depth + 1, Q);
-
-        // Calculate the leading sign bit constraints by examining the
-        // denominator.  Given that the denominator is positive, there are two
-        // cases:
-        //
-        //  1. the numerator is positive. The result range is [0,C) and [0,C) u<
-        //     (1 << ceilLogBase2(C)).
-        //
-        //  2. the numerator is negative. Then the result range is (-C,0] and
-        //     integers in (-C,0] are either 0 or >u (-1 << ceilLogBase2(C)).
-        //
-        // Thus a lower bound on the number of sign bits is `TyBits -
-        // ceilLogBase2(C)`.
-
-        unsigned ResBits = TyBits - Denominator->ceilLogBase2();
-        return std::max(NumrBits, ResBits);
+        if (Denominator->isStrictlyPositive()) {
+          // Calculate the leading sign bit constraints by examining the
+          // denominator.  Given that the denominator is positive, there are two
+          // cases:
+          //
+          //  1. The numerator is positive. The result range is [0,C) and
+          //     [0,C) u< (1 << ceilLogBase2(C)).
+          //
+          //  2. The numerator is negative. Then the result range is (-C,0] and
+          //     integers in (-C,0] are either 0 or >u (-1 << ceilLogBase2(C)).
+          //
+          // Thus a lower bound on the number of sign bits is `TyBits -
+          // ceilLogBase2(C)`.
+
+          unsigned ResBits = TyBits - Denominator->ceilLogBase2();
+          Tmp = std::max(Tmp, ResBits);
+        }
       }
-      break;
+      return Tmp;
     }
 
     case Instruction::AShr: {


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