[PATCH] D124327: [SCCP] Add initial support for propagation through freeze.

[Florian Hahn via Phabricator via llvm-commits]

fhahn created this revision.
fhahn added reviewers: nlopes, efriedma, nikic, aqjune.
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This patch implements initial support for freeze instructions in
[IP]SCCP.

If the operand is known to be undef, exit early and wait until it
changes. If it stays undef until the end of solving, resolvedUndefsIn
will take care of handling it. At the moment, it will be marked as
overdefined.

Otherwise just merge in the value of the operand.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D124327

Files:
  llvm/lib/Transforms/Utils/SCCPSolver.cpp
  llvm/test/Transforms/SCCP/freeze.ll


Index: llvm/test/Transforms/SCCP/freeze.ll
===================================================================
--- llvm/test/Transforms/SCCP/freeze.ll
+++ llvm/test/Transforms/SCCP/freeze.ll
@@ -43,17 +43,12 @@
 ; CHECK-LABEL: @propagate_range_from_and_through_freeze(
 ; CHECK-NEXT:    [[AND:%.*]] = and i32 [[X:%.*]], 3
 ; CHECK-NEXT:    [[AND_FR:%.*]] = freeze i32 [[AND]]
-; CHECK-NEXT:    [[F_1:%.*]] = icmp eq i32 [[AND_FR]], 100
-; CHECK-NEXT:    call void @use(i1 [[F_1]])
-; CHECK-NEXT:    [[T_1:%.*]] = icmp ule i32 [[AND_FR]], 3
-; CHECK-NEXT:    call void @use(i1 [[T_1]])
-; CHECK-NEXT:    [[F_2:%.*]] = icmp ugt i32 [[AND_FR]], 3
-; CHECK-NEXT:    call void @use(i1 [[F_2]])
+; CHECK-NEXT:    call void @use(i1 false)
+; CHECK-NEXT:    call void @use(i1 true)
+; CHECK-NEXT:    call void @use(i1 false)
 ; CHECK-NEXT:    [[C_1:%.*]] = icmp eq i32 [[AND_FR]], [[Y:%.*]]
 ; CHECK-NEXT:    call void @use(i1 [[C_1]])
-; CHECK-NEXT:    [[R_1:%.*]] = xor i1 [[T_1]], [[F_1]]
-; CHECK-NEXT:    [[R_2:%.*]] = xor i1 [[R_1]], [[F_2]]
-; CHECK-NEXT:    [[R_3:%.*]] = xor i1 [[R_2]], [[C_1]]
+; CHECK-NEXT:    [[R_3:%.*]] = xor i1 true, [[C_1]]
 ; CHECK-NEXT:    ret i1 [[R_3]]
 ;
   %and = and i32 %x, 3
@@ -84,10 +79,7 @@
 ; CHECK:       exit:
 ; CHECK-NEXT:    [[P:%.*]] = phi i32 [ 10, [[TRUE_1]] ], [ 20, [[TRUE_2]] ], [ undef, [[FALSE]] ]
 ; CHECK-NEXT:    [[P_FR:%.*]] = freeze i32 [[P]]
-; CHECK-NEXT:    [[T_1:%.*]] = icmp ule i32 [[P_FR]], 20
-; CHECK-NEXT:    [[T_2:%.*]] = icmp uge i32 [[P_FR]], 10
-; CHECK-NEXT:    [[RES:%.*]] = xor i1 [[T_1]], [[T_2]]
-; CHECK-NEXT:    ret i1 [[RES]]
+; CHECK-NEXT:    ret i1 false
 ;
   br i1 %c.1, label %true.1, label %false
 
Index: llvm/lib/Transforms/Utils/SCCPSolver.cpp
===================================================================
--- llvm/lib/Transforms/Utils/SCCPSolver.cpp
+++ llvm/lib/Transforms/Utils/SCCPSolver.cpp
@@ -322,6 +322,16 @@
   }
   void visitFenceInst(FenceInst &I) { /*returns void*/
   }
+  void visitFreezeInst(FreezeInst &I) {
+    auto &OpV = getValueState(I.getOperand(0));
+    // If the operand is known to be undef, wait until it changes. If it stays
+    // undef until the end of solving, resolvedUndefsIn will handle it.
+    if (OpV.isUndef())
+      return;
+
+    auto &LV = getValueState(&I);
+    mergeInValue(LV, &I, OpV);
+  }
 
   void visitInstruction(Instruction &I);
 


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