[ConstraintElim] Add support for trunc nsw/nuw

Author: dtcxzyw

llvm/lib/Transforms/Scalar/ConstraintElimination.cpp

@@ -521,6 +521,9 @@ static Decomposition decompose(Value *V,
     else if (match(V, m_NNegZExt(m_Value(Op0)))) {
       V = Op0;
       IsKnownNonNegative = true;
+    } else if (match(V, m_NSWTrunc(m_Value(Op0)))) {
+      if (Op0->getType()->getScalarSizeInBits() <= 64)
+        V = Op0;
     }
 
     if (match(V, m_NSWAdd(m_Value(Op0), m_Value(Op1))))
@@ -558,12 +561,19 @@ static Decomposition decompose(Value *V,
   if (match(V, m_ZExt(m_Value(Op0)))) {
     IsKnownNonNegative = true;
     V = Op0;
-  }
-
-  if (match(V, m_SExt(m_Value(Op0)))) {
+  } else if (match(V, m_SExt(m_Value(Op0)))) {
     V = Op0;
     Preconditions.emplace_back(CmpInst::ICMP_SGE, Op0,
                                ConstantInt::get(Op0->getType(), 0));
+  } else if (auto *Trunc = dyn_cast<TruncInst>(V)) {
+    if (Trunc->getSrcTy()->getScalarSizeInBits() <= 64) {
+      if (Trunc->hasNoUnsignedWrap() || Trunc->hasNoSignedWrap()) {
+        V = Trunc->getOperand(0);
+        if (!Trunc->hasNoUnsignedWrap())
+          Preconditions.emplace_back(CmpInst::ICMP_SGE, V,
+                                     ConstantInt::get(V->getType(), 0));
+      }
+    }
   }
 
   Value *Op1;

llvm/test/Transforms/ConstraintElimination/trunc.ll

@@ -9,8 +9,7 @@ define i1 @test_icmp_ult_zext_icmp_trunc_nuw(i16 %x, i32 %y) {
 ; CHECK-NEXT:    br i1 [[COND]], label %[[IF_THEN:.*]], label %[[IF_ELSE:.*]]
 ; CHECK:       [[IF_THEN]]:
 ; CHECK-NEXT:    [[CONV:%.*]] = trunc nuw i32 [[Y]] to i16
-; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i16 [[X]], [[CONV]]
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    ret i1 false
 ; CHECK:       [[IF_ELSE]]:
 ; CHECK-NEXT:    ret i1 false
 ;
@@ -35,8 +34,7 @@ define i1 @test_icmp_slt_sext_icmp_trunc_nsw(i16 %x, i32 %y) {
 ; CHECK-NEXT:    br i1 [[COND]], label %[[IF_THEN:.*]], label %[[IF_ELSE:.*]]
 ; CHECK:       [[IF_THEN]]:
 ; CHECK-NEXT:    [[CONV:%.*]] = trunc nsw i32 [[Y]] to i16
-; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i16 [[X]], [[CONV]]
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    ret i1 false
 ; CHECK:       [[IF_ELSE]]:
 ; CHECK-NEXT:    ret i1 false
 ;
@@ -63,8 +61,7 @@ define i1 @test_icmp_ult_trunc_nsw_nneg_icmp_trunc_nuw(i64 %x, i32 %y) {
 ; CHECK-NEXT:    br i1 [[AND]], label %[[IF_THEN:.*]], label %[[IF_ELSE:.*]]
 ; CHECK:       [[IF_THEN]]:
 ; CHECK-NEXT:    [[CONV:%.*]] = zext i32 [[Y]] to i64
-; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i64 [[X]], [[CONV]]
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    ret i1 false
 ; CHECK:       [[IF_ELSE]]:
 ; CHECK-NEXT:    ret i1 false
 ;
@@ -102,8 +99,7 @@ define i1 @test2(i32 %n) {
 ; CHECK-NEXT:    br i1 [[COND2]], label %[[FOR_BODY]], label %[[FOR_END:.*]]
 ; CHECK:       [[FOR_END]]:
 ; CHECK-NEXT:    [[TRUNC:%.*]] = trunc nsw i64 [[INDVAR_NEXT]] to i32
-; CHECK-NEXT:    [[RES:%.*]] = icmp sgt i32 [[N]], [[TRUNC]]
-; CHECK-NEXT:    ret i1 [[RES]]
+; CHECK-NEXT:    ret i1 true
 ; CHECK:       [[IF_ELSE]]:
 ; CHECK-NEXT:    ret i1 false
 ;