[RISCV][CodeGenPrepare] Remove duplicated transform for zext. NFC. (#72053)

After #71534 and #72052, the transform `zext -> zext nneg` in
`RISCVCodeGenPrepare` is redundant.

Author: dtcxzyw

llvm/lib/Target/RISCV/RISCVCodeGenPrepare.cpp

@@ -28,8 +28,6 @@ using namespace llvm;
 #define DEBUG_TYPE "riscv-codegenprepare"
 #define PASS_NAME "RISC-V CodeGenPrepare"
 
-STATISTIC(NumZExtToSExt, "Number of SExt instructions converted to ZExt");
-
 namespace {
 
 class RISCVCodeGenPrepare : public FunctionPass,
@@ -52,49 +50,11 @@ class RISCVCodeGenPrepare : public FunctionPass,
   }
 
   bool visitInstruction(Instruction &I) { return false; }
-  bool visitZExtInst(ZExtInst &I);
   bool visitAnd(BinaryOperator &BO);
 };
 
 } // end anonymous namespace
 
-bool RISCVCodeGenPrepare::visitZExtInst(ZExtInst &ZExt) {
-  if (!ST->is64Bit())
-    return false;
-
-  if (ZExt.hasNonNeg())
-    return false;
-
-  Value *Src = ZExt.getOperand(0);
-
-  // We only care about ZExt from i32 to i64.
-  if (!ZExt.getType()->isIntegerTy(64) || !Src->getType()->isIntegerTy(32))
-    return false;
-
-  // Look for an opportunity to infer nneg on a zext if we can determine that
-  // the sign bit of X is zero via a dominating condition. This often occurs
-  // with widened induction variables.
-  if (isImpliedByDomCondition(ICmpInst::ICMP_SGE, Src,
-                              Constant::getNullValue(Src->getType()), &ZExt,
-                              *DL).value_or(false)) {
-    ZExt.setNonNeg(true);
-    ++NumZExtToSExt;
-    return true;
-  }
-
-  // Convert (zext (abs(i32 X, i1 1))) -> (zext nneg (abs(i32 X, i1 1))). If abs of
-  // INT_MIN is poison, the sign bit is zero.
-  // TODO: Move this to instcombine now that we have zext nneg in IR.
-  using namespace PatternMatch;
-  if (match(Src, m_Intrinsic<Intrinsic::abs>(m_Value(), m_One()))) {
-    ZExt.setNonNeg(true);
-    ++NumZExtToSExt;
-    return true;
-  }
-
-  return false;
-}
-
 // Try to optimize (i64 (and (zext/sext (i32 X), C1))) if C1 has bit 31 set,
 // but bits 63:32 are zero. If we know that bit 31 of X is 0, we can fill
 // the upper 32 bits with ones.

llvm/test/CodeGen/RISCV/iabs.ll

@@ -494,7 +494,7 @@ define i64 @zext_abs32(i32 %x) {
 ; RV64ZBB-NEXT:    max a0, a0, a1
 ; RV64ZBB-NEXT:    ret
   %abs = tail call i32 @llvm.abs.i32(i32 %x, i1 true)
-  %zext = zext i32 %abs to i64
+  %zext = zext nneg i32 %abs to i64
   ret i64 %zext
 }
 

llvm/test/CodeGen/RISCV/riscv-codegenprepare-asm.ll

@@ -24,7 +24,7 @@ entry:
   br i1 %cmp3, label %for.body.preheader, label %for.cond.cleanup
 
 for.body.preheader:                               ; preds = %entry
-  %wide.trip.count = zext i32 %n to i64
+  %wide.trip.count = zext nneg i32 %n to i64
   br label %for.body
 
 for.cond.cleanup:                                 ; preds = %for.body, %entry
@@ -84,7 +84,7 @@ entry:
   br i1 %cmp3, label %for.body.preheader, label %for.cond.cleanup
 
 for.body.preheader:                               ; preds = %entry
-  %wide.trip.count = zext i32 %n to i64
+  %wide.trip.count = zext nneg i32 %n to i64
   %xtraiter = and i64 %wide.trip.count, 1
   %0 = icmp eq i32 %n, 1
   br i1 %0, label %for.cond.cleanup.loopexit.unr-lcssa, label %for.body.preheader.new

llvm/test/CodeGen/RISCV/riscv-codegenprepare.ll

@@ -1,57 +1,6 @@
 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
 ; RUN: opt %s -S -riscv-codegenprepare -mtriple=riscv64 | FileCheck %s
 
-; Test that we can convert the %wide.trip.count zext to a sext. The dominating
-; condition %cmp3 ruled out %n being negative.
-define void @test1(ptr nocapture noundef %a, i32 noundef signext %n) {
-; CHECK-LABEL: @test1(
-; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[CMP3:%.*]] = icmp sgt i32 [[N:%.*]], 0
-; CHECK-NEXT:    br i1 [[CMP3]], label [[FOR_BODY_PREHEADER:%.*]], label [[FOR_COND_CLEANUP:%.*]]
-; CHECK:       for.body.preheader:
-; CHECK-NEXT:    [[WIDE_TRIP_COUNT:%.*]] = zext nneg i32 [[N]] to i64
-; CHECK-NEXT:    br label [[FOR_BODY:%.*]]
-; CHECK:       for.cond.cleanup.loopexit:
-; CHECK-NEXT:    br label [[FOR_COND_CLEANUP]]
-; CHECK:       for.cond.cleanup:
-; CHECK-NEXT:    ret void
-; CHECK:       for.body:
-; CHECK-NEXT:    [[LSR_IV5:%.*]] = phi i64 [ [[WIDE_TRIP_COUNT]], [[FOR_BODY_PREHEADER]] ], [ [[LSR_IV_NEXT:%.*]], [[FOR_BODY]] ]
-; CHECK-NEXT:    [[LSR_IV:%.*]] = phi ptr [ [[A:%.*]], [[FOR_BODY_PREHEADER]] ], [ [[UGLYGEP:%.*]], [[FOR_BODY]] ]
-; CHECK-NEXT:    [[TMP0:%.*]] = load i32, ptr [[LSR_IV]], align 4
-; CHECK-NEXT:    [[ADD:%.*]] = add nsw i32 [[TMP0]], 4
-; CHECK-NEXT:    store i32 [[ADD]], ptr [[LSR_IV]], align 4
-; CHECK-NEXT:    [[UGLYGEP]] = getelementptr i8, ptr [[LSR_IV]], i64 4
-; CHECK-NEXT:    [[LSR_IV_NEXT]] = add nsw i64 [[LSR_IV5]], -1
-; CHECK-NEXT:    [[EXITCOND_NOT:%.*]] = icmp eq i64 [[LSR_IV_NEXT]], 0
-; CHECK-NEXT:    br i1 [[EXITCOND_NOT]], label [[FOR_COND_CLEANUP_LOOPEXIT:%.*]], label [[FOR_BODY]]
-;
-entry:
-  %cmp3 = icmp sgt i32 %n, 0
-  br i1 %cmp3, label %for.body.preheader, label %for.cond.cleanup
-
-for.body.preheader:                               ; preds = %entry
-  %wide.trip.count = zext i32 %n to i64
-  br label %for.body
-
-for.cond.cleanup.loopexit:                        ; preds = %for.body
-  br label %for.cond.cleanup
-
-for.cond.cleanup:                                 ; preds = %for.cond.cleanup.loopexit, %entry
-  ret void
-
-for.body:                                         ; preds = %for.body.preheader, %for.body
-  %lsr.iv5 = phi i64 [ %wide.trip.count, %for.body.preheader ], [ %lsr.iv.next, %for.body ]
-  %lsr.iv = phi ptr [ %a, %for.body.preheader ], [ %uglygep, %for.body ]
-  %0 = load i32, ptr %lsr.iv, align 4
-  %add = add nsw i32 %0, 4
-  store i32 %add, ptr %lsr.iv, align 4
-  %uglygep = getelementptr i8, ptr %lsr.iv, i64 4
-  %lsr.iv.next = add nsw i64 %lsr.iv5, -1
-  %exitcond.not = icmp eq i64 %lsr.iv.next, 0
-  br i1 %exitcond.not, label %for.cond.cleanup.loopexit, label %for.body
-}
-
 ; Make sure we convert the 4294967294 in for.body.preheader.new to -2 based on
 ; the upper 33 bits being zero by the dominating condition %cmp3.
 define void @test2(ptr nocapture noundef %a, i32 noundef signext %n) {
@@ -101,7 +50,7 @@ entry:
   br i1 %cmp3, label %for.body.preheader, label %for.cond.cleanup
 
 for.body.preheader:                               ; preds = %entry
-  %wide.trip.count = zext i32 %n to i64
+  %wide.trip.count = zext nneg i32 %n to i64
   %xtraiter = and i64 %wide.trip.count, 1
   %0 = icmp eq i32 %n, 1
   br i1 %0, label %for.cond.cleanup.loopexit.unr-lcssa, label %for.body.preheader.new