[llvm] be20eae - Look through invertible recurrences in isKnownNonEqual

[Philip Reames via llvm-commits]

Author: Philip Reames
Date: 2021-04-20T10:52:22-07:00
New Revision: be20eae25f50f5ef648aeefa1143e1c31e4410fc

URL: https://github.com/llvm/llvm-project/commit/be20eae25f50f5ef648aeefa1143e1c31e4410fc
DIFF: https://github.com/llvm/llvm-project/commit/be20eae25f50f5ef648aeefa1143e1c31e4410fc.diff

LOG: Look through invertible recurrences in isKnownNonEqual

This extends the phi handling in isKnownNonEqual with a special case based on invertible recurrences. If we can prove the recurrence is invertible (which many common ones are), we can recurse through the start operands of the recurrence skipping the phi cycle.

(Side note: Instcombine currently does not push back through these cases. I will implement that in a follow up change w/separate review.)

Differential Revision: https://reviews.llvm.org/D99912

Added: 
    

Modified: 
    llvm/lib/Analysis/ValueTracking.cpp
    llvm/test/Analysis/ValueTracking/known-non-equal.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 46aa84f72aaf..8dbf1f78a2e1 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -2580,6 +2580,35 @@ static Optional<unsigned> getInvertibleOperand(const Operator *Op1,
     if (Op1->getOperand(0)->getType() == Op2->getOperand(0)->getType())
       return 0;
     break;
+  case Instruction::PHI: {
+    const PHINode *PN1 = cast<PHINode>(Op1);
+    const PHINode *PN2 = cast<PHINode>(Op2);
+
+    // If PN1 and PN2 are both recurrences, can we prove the entire recurrences
+    // are a single invertible function of the start values? Note that repeated
+    // application of an invertible function is also invertible
+    BinaryOperator *BO1 = nullptr;
+    Value *Start1 = nullptr, *Step1 = nullptr;
+    BinaryOperator *BO2 = nullptr;
+    Value *Start2 = nullptr, *Step2 = nullptr;
+    if (PN1->getParent() != PN2->getParent() ||
+        !matchSimpleRecurrence(PN1, BO1, Start1, Step1) ||
+        !matchSimpleRecurrence(PN2, BO2, Start2, Step2))
+      break;
+
+    Optional<unsigned> Idx = getInvertibleOperand(cast<Operator>(BO1),
+                                                  cast<Operator>(BO2));
+    if (!Idx || *Idx != 0)
+      break;
+    assert(BO1->getOperand(*Idx) == PN1 && BO2->getOperand(*Idx) == PN2);
+
+    if (PN1->getOperand(0) == BO1) {
+      assert(PN2->getOperand(0) == BO2);
+      return 1;
+    }
+    assert(PN1->getOperand(1) == BO1 && PN2->getOperand(1) == BO2);
+    return 0;
+  }
   }
   return None;
 }

diff  --git a/llvm/test/Analysis/ValueTracking/known-non-equal.ll b/llvm/test/Analysis/ValueTracking/known-non-equal.ll
index 257a0a255af3..870af630d6bb 100644
--- a/llvm/test/Analysis/ValueTracking/known-non-equal.ll
+++ b/llvm/test/Analysis/ValueTracking/known-non-equal.ll
@@ -598,8 +598,7 @@ define i1 @recurrence_add_neq(i8 %A) {
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp ne i64 [[IV_NEXT]], 10
 ; CHECK-NEXT:    br i1 [[CMP]], label [[LOOP]], label [[EXIT:%.*]]
 ; CHECK:       exit:
-; CHECK-NEXT:    [[RES:%.*]] = icmp eq i8 [[A_IV]], [[B_IV]]
-; CHECK-NEXT:    ret i1 [[RES]]
+; CHECK-NEXT:    ret i1 false
 ;
 entry:
   %B = add i8 %A, 1
@@ -775,8 +774,7 @@ define i1 @recurrence_add_neq_phi_order(i8 %A) {
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp ne i64 [[IV_NEXT]], 10
 ; CHECK-NEXT:    br i1 [[CMP]], label [[LOOP]], label [[EXIT:%.*]]
 ; CHECK:       exit:
-; CHECK-NEXT:    [[RES:%.*]] = icmp eq i8 [[A_IV]], [[B_IV]]
-; CHECK-NEXT:    ret i1 [[RES]]
+; CHECK-NEXT:    ret i1 false
 ;
 entry:
   %B = add i8 %A, 1
@@ -810,8 +808,7 @@ define i1 @recurrence_sub_neq(i8 %A) {
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp ne i64 [[IV_NEXT]], 10
 ; CHECK-NEXT:    br i1 [[CMP]], label [[LOOP]], label [[EXIT:%.*]]
 ; CHECK:       exit:
-; CHECK-NEXT:    [[RES:%.*]] = icmp eq i8 [[A_IV]], [[B_IV]]
-; CHECK-NEXT:    ret i1 [[RES]]
+; CHECK-NEXT:    ret i1 false
 ;
 entry:
   %B = add i8 %A, 1
@@ -912,8 +909,7 @@ define i1 @recurrence_mul_neq(i8 %A) {
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp ne i64 [[IV_NEXT]], 10
 ; CHECK-NEXT:    br i1 [[CMP]], label [[LOOP]], label [[EXIT:%.*]]
 ; CHECK:       exit:
-; CHECK-NEXT:    [[RES:%.*]] = icmp eq i8 [[A_IV]], [[B_IV]]
-; CHECK-NEXT:    ret i1 [[RES]]
+; CHECK-NEXT:    ret i1 false
 ;
 entry:
   %B = add i8 %A, 1
@@ -1049,8 +1045,7 @@ define i1 @recurrence_shl_neq(i8 %A) {
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp ne i64 [[IV_NEXT]], 10
 ; CHECK-NEXT:    br i1 [[CMP]], label [[LOOP]], label [[EXIT:%.*]]
 ; CHECK:       exit:
-; CHECK-NEXT:    [[RES:%.*]] = icmp eq i8 [[A_IV]], [[B_IV]]
-; CHECK-NEXT:    ret i1 [[RES]]
+; CHECK-NEXT:    ret i1 false
 ;
 entry:
   %B = add i8 %A, 1
@@ -1186,8 +1181,7 @@ define i1 @recurrence_lshr_neq(i8 %A) {
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp ne i64 [[IV_NEXT]], 10
 ; CHECK-NEXT:    br i1 [[CMP]], label [[LOOP]], label [[EXIT:%.*]]
 ; CHECK:       exit:
-; CHECK-NEXT:    [[RES:%.*]] = icmp eq i8 [[A_IV]], [[B_IV]]
-; CHECK-NEXT:    ret i1 [[RES]]
+; CHECK-NEXT:    ret i1 false
 ;
 entry:
   %B = add i8 %A, 1
@@ -1323,8 +1317,7 @@ define i1 @recurrence_ashr_neq(i8 %A) {
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp ne i64 [[IV_NEXT]], 10
 ; CHECK-NEXT:    br i1 [[CMP]], label [[LOOP]], label [[EXIT:%.*]]
 ; CHECK:       exit:
-; CHECK-NEXT:    [[RES:%.*]] = icmp eq i8 [[A_IV]], [[B_IV]]
-; CHECK-NEXT:    ret i1 [[RES]]
+; CHECK-NEXT:    ret i1 false
 ;
 entry:
   %B = add i8 %A, 1