[llvm] [InstCombine] Remove `foldSPFofSPF` (PR #146736)

[Yingwei Zheng via llvm-commits]

https://github.com/dtcxzyw created https://github.com/llvm/llvm-project/pull/146736

This fold should be covered by `foldMinMaxSharedOp/foldMinimumMaximumSharedOp`. And it has the same poison-propagation problem as https://github.com/llvm/llvm-project/issues/143120.


>From 8a0f7780f39e6a7f03886dd022a4f7cfa8a2e604 Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Wed, 2 Jul 2025 23:50:01 +0800
Subject: [PATCH] [InstCombine] Remove `foldSPFofSPF`

---
 .../InstCombine/InstCombineInternal.h         |  3 --
 .../InstCombine/InstCombineSelect.cpp         | 32 -------------------
 2 files changed, 35 deletions(-)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
index 9adde8094d44d..65daeecba061e 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
+++ b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
@@ -782,9 +782,6 @@ class LLVM_LIBRARY_VISIBILITY InstCombinerImpl final
   Instruction *foldSelectEqualityTest(SelectInst &SI);
   Instruction *foldSelectOpOp(SelectInst &SI, Instruction *TI, Instruction *FI);
   Instruction *foldSelectIntoOp(SelectInst &SI, Value *, Value *);
-  Instruction *foldSPFofSPF(Instruction *Inner, SelectPatternFlavor SPF1,
-                            Value *A, Value *B, Instruction &Outer,
-                            SelectPatternFlavor SPF2, Value *C);
   Instruction *foldSelectInstWithICmp(SelectInst &SI, ICmpInst *ICI);
   Value *foldSelectWithConstOpToBinOp(ICmpInst *Cmp, Value *TrueVal,
                                       Value *FalseVal);
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
index 73ba0f78e8053..5a0cd443b1701 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -2051,27 +2051,6 @@ Instruction *InstCombinerImpl::foldSelectInstWithICmp(SelectInst &SI,
   return Changed ? &SI : nullptr;
 }
 
-/// We have an SPF (e.g. a min or max) of an SPF of the form:
-///   SPF2(SPF1(A, B), C)
-Instruction *InstCombinerImpl::foldSPFofSPF(Instruction *Inner,
-                                            SelectPatternFlavor SPF1, Value *A,
-                                            Value *B, Instruction &Outer,
-                                            SelectPatternFlavor SPF2,
-                                            Value *C) {
-  if (Outer.getType() != Inner->getType())
-    return nullptr;
-
-  if (C == A || C == B) {
-    // MAX(MAX(A, B), B) -> MAX(A, B)
-    // MIN(MIN(a, b), a) -> MIN(a, b)
-    // TODO: This could be done in instsimplify.
-    if (SPF1 == SPF2 && SelectPatternResult::isMinOrMax(SPF1))
-      return replaceInstUsesWith(Outer, Inner);
-  }
-
-  return nullptr;
-}
-
 /// Turn select C, (X + Y), (X - Y) --> (X + (select C, Y, (-Y))).
 /// This is even legal for FP.
 static Instruction *foldAddSubSelect(SelectInst &SI,
@@ -4157,17 +4136,6 @@ Instruction *InstCombinerImpl::visitSelectInst(SelectInst &SI) {
     Instruction::CastOps CastOp;
     SelectPatternResult SPR = matchSelectPattern(&SI, LHS, RHS, &CastOp);
     auto SPF = SPR.Flavor;
-    if (SPF) {
-      Value *LHS2, *RHS2;
-      if (SelectPatternFlavor SPF2 = matchSelectPattern(LHS, LHS2, RHS2).Flavor)
-        if (Instruction *R = foldSPFofSPF(cast<Instruction>(LHS), SPF2, LHS2,
-                                          RHS2, SI, SPF, RHS))
-          return R;
-      if (SelectPatternFlavor SPF2 = matchSelectPattern(RHS, LHS2, RHS2).Flavor)
-        if (Instruction *R = foldSPFofSPF(cast<Instruction>(RHS), SPF2, LHS2,
-                                          RHS2, SI, SPF, LHS))
-          return R;
-    }
 
     if (SelectPatternResult::isMinOrMax(SPF)) {
       // Canonicalize so that