[llvm] 4d0c0e6 - [SCEV] `createNodeForSelectOrPHIInstWithICmpInstCond()`: generalize eq handling

[Roman Lebedev via llvm-commits]

Author: Roman Lebedev
Date: 2022-02-11T21:58:19+03:00
New Revision: 4d0c0e6cc250e0637548f8a8519a95f15b6fab2e

URL: https://github.com/llvm/llvm-project/commit/4d0c0e6cc250e0637548f8a8519a95f15b6fab2e
DIFF: https://github.com/llvm/llvm-project/commit/4d0c0e6cc250e0637548f8a8519a95f15b6fab2e.diff

LOG: [SCEV] `createNodeForSelectOrPHIInstWithICmpInstCond()`: generalize eq handling

The current logic was: https://alive2.llvm.org/ce/z/j8muXk
but in reality the offset to the Y in the 'true' hand
does not need to exist: https://alive2.llvm.org/ce/z/MNQ7DZ
https://alive2.llvm.org/ce/z/S2pMQD

To catch that, instead of computing the Y's in both
hands and checking their equality, compute Y and C,
and check that C is 0 or 1.

Added: 
    

Modified: 
    llvm/lib/Analysis/ScalarEvolution.cpp
    llvm/test/Analysis/ScalarEvolution/logical-operations.ll
    llvm/test/Analysis/ScalarEvolution/min-max-exprs.ll
    polly/test/ForwardOpTree/changed-kind.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 8b479da3dfcf5..84680ff6b9b30 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -5952,21 +5952,20 @@ const SCEV *ScalarEvolution::createNodeForSelectOrPHIInstWithICmpInstCond(
     }
     break;
   case ICmpInst::ICMP_NE:
-    // n != 0 ? n+x : 1+x  ->  n == 0 ? 1+x : n+x
+    // x != 0 ? x+y : C+y  ->  x == 0 ? C+y : x+y
     std::swap(TrueVal, FalseVal);
     LLVM_FALLTHROUGH;
   case ICmpInst::ICMP_EQ:
-    // n == 0 ? 1+x : n+x  ->  umax(n, 1)+x
+    // x == 0 ? C+y : x+y  ->  umax(x, C)+y   iff C u<= 1
     if (getTypeSizeInBits(LHS->getType()) <= getTypeSizeInBits(I->getType()) &&
         isa<ConstantInt>(RHS) && cast<ConstantInt>(RHS)->isZero()) {
-      const SCEV *One = getOne(I->getType());
-      const SCEV *LS = getNoopOrZeroExtend(getSCEV(LHS), I->getType());
-      const SCEV *LA = getSCEV(TrueVal);
-      const SCEV *RA = getSCEV(FalseVal);
-      const SCEV *LDiff = getMinusSCEV(LA, One);
-      const SCEV *RDiff = getMinusSCEV(RA, LS);
-      if (LDiff == RDiff)
-        return getAddExpr(getUMaxExpr(One, LS), LDiff);
+      const SCEV *X = getNoopOrZeroExtend(getSCEV(LHS), I->getType());
+      const SCEV *TrueValExpr = getSCEV(TrueVal);    // C+y
+      const SCEV *FalseValExpr = getSCEV(FalseVal);  // x+y
+      const SCEV *Y = getMinusSCEV(FalseValExpr, X); // y = (x+y)-x
+      const SCEV *C = getMinusSCEV(TrueValExpr, Y);  // C = (C+y)-y
+      if (isa<SCEVConstant>(C) && cast<SCEVConstant>(C)->getAPInt().ule(1))
+        return getAddExpr(getUMaxExpr(X, C), Y);
     }
     break;
   default:

diff  --git a/llvm/test/Analysis/ScalarEvolution/logical-operations.ll b/llvm/test/Analysis/ScalarEvolution/logical-operations.ll
index a7a9413f53fd5..8f04e02f61bab 100644
--- a/llvm/test/Analysis/ScalarEvolution/logical-operations.ll
+++ b/llvm/test/Analysis/ScalarEvolution/logical-operations.ll
@@ -478,7 +478,7 @@ define i32 @umin_seq_x_y_tautological(i32 %x, i32 %y) {
 ; CHECK-NEXT:    %umin = call i32 @llvm.umin.i32(i32 %y, i32 %x)
 ; CHECK-NEXT:    --> (%x umin %y) U: full-set S: full-set
 ; CHECK-NEXT:    %r = select i1 %umin.is.zero, i32 0, i32 %umin
-; CHECK-NEXT:    --> %r U: full-set S: full-set
+; CHECK-NEXT:    --> (%x umin %y) U: full-set S: full-set
 ; CHECK-NEXT:  Determining loop execution counts for: @umin_seq_x_y_tautological
 ;
   %umin = call i32 @llvm.umin(i32 %y, i32 %x)
@@ -492,7 +492,7 @@ define i32 @umin_seq_x_y_tautological_wrongtype(i32 %x, i32 %y) {
 ; CHECK-NEXT:    %umax = call i32 @llvm.umax.i32(i32 %y, i32 %x)
 ; CHECK-NEXT:    --> (%x umax %y) U: full-set S: full-set
 ; CHECK-NEXT:    %r = select i1 %umax.is.zero, i32 0, i32 %umax
-; CHECK-NEXT:    --> %r U: full-set S: full-set
+; CHECK-NEXT:    --> (%x umax %y) U: full-set S: full-set
 ; CHECK-NEXT:  Determining loop execution counts for: @umin_seq_x_y_tautological_wrongtype
 ;
   %umax = call i32 @llvm.umax(i32 %y, i32 %x)

diff  --git a/llvm/test/Analysis/ScalarEvolution/min-max-exprs.ll b/llvm/test/Analysis/ScalarEvolution/min-max-exprs.ll
index d0339ecd13cd3..208f369ac4a90 100644
--- a/llvm/test/Analysis/ScalarEvolution/min-max-exprs.ll
+++ b/llvm/test/Analysis/ScalarEvolution/min-max-exprs.ll
@@ -127,7 +127,7 @@ define i8 @umax_basic_eq_off0(i8 %x, i8 %y) {
 ; CHECK-NEXT:    %rhs = add i8 %x, %y
 ; CHECK-NEXT:    --> (%x + %y) U: full-set S: full-set
 ; CHECK-NEXT:    %r = select i1 %x.is.zero, i8 %lhs, i8 %rhs
-; CHECK-NEXT:    --> %r U: full-set S: full-set
+; CHECK-NEXT:    --> (%x + %y) U: full-set S: full-set
 ; CHECK-NEXT:  Determining loop execution counts for: @umax_basic_eq_off0
 ;
   %x.is.zero = icmp eq i8 %x, 0

diff  --git a/polly/test/ForwardOpTree/changed-kind.ll b/polly/test/ForwardOpTree/changed-kind.ll
index a66ba557d2a80..bf81f51021b5d 100644
--- a/polly/test/ForwardOpTree/changed-kind.ll
+++ b/polly/test/ForwardOpTree/changed-kind.ll
@@ -43,12 +43,5 @@ lor.end93:
 
 
 ; CHECK: Statistics {
-; CHECK:     Reloads: 1
-; CHECK: }
-
-; CHECK: After statements {
-; CHECK:     Stmt_lor_end93
-; CHECK-NEXT:        ReadAccess :=       [Reduction Type: NONE] [Scalar: 1]
-; CHECK-NEXT:            { Stmt_lor_end93[] -> MemRef3[] };
-; CHECK-NEXT:       new: { Stmt_lor_end93[] -> MemRef_c[0] };
+; CHECK:     Reloads: 0
 ; CHECK: }