[llvm] [LoopIdiomVectorize] Recognize and transform minidx pattern (PR #144987)

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``````````bash
git-clang-format --diff HEAD~1 HEAD --extensions cpp -- llvm/lib/Transforms/Vectorize/LoopIdiomVectorize.cpp
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``````````diff
diff --git a/llvm/lib/Transforms/Vectorize/LoopIdiomVectorize.cpp b/llvm/lib/Transforms/Vectorize/LoopIdiomVectorize.cpp
index 59e407cc8..b2a152710 100644
--- a/llvm/lib/Transforms/Vectorize/LoopIdiomVectorize.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoopIdiomVectorize.cpp
@@ -317,7 +317,8 @@ bool LoopIdiomVectorize::recognizeMinIdxPattern() {
   // 1. add(sext(sub(0 - SecondIndex)), sext(FirstIndex))
   // 2. add(sext(FirstIndex), sext(sub(0 - SecondIndex)))
   // This depends on whether canonicalization has been done or not.
-  // TODO: Handle the case where there is no sign extension and return type is i64.
+  // TODO: Handle the case where there is no sign extension and return type is
+  // i64.
   if (match(ICmpSLTFirstVal, m_Add(m_SExt(m_Sub(m_ZeroInt(), m_Value())),
                                    (m_SExt(m_Value()))))) {
     FirstIndex = dyn_cast<Instruction>(ICmpSLTFirstVal)->getOperand(1);
@@ -442,24 +443,23 @@ bool LoopIdiomVectorize::transformMinIdxPattern(
   auto *VecTy = ScalableVectorType::get(
       LoadType, VF); // This is the vector type for i32 values
 
-
   // High-level overview of the transformation:
   // We divide the process in three phases:
   // In the first phase, we process a chunk which is not multiple of VF.
-  // We do this by rounding down the `SecondIndex` to the nearest multiple of VF.
-  // The minimum value and the index of the minimum value are computed for this chunk.
-  // In the second phase, we process all chunks which are multiple of VF.
-  // In the third phase, we process the last chunk which is not multiple of VF.
-  // The third phase is required because the FirstIndex is necessary to start from zero
-  // thus we take max(0, FirstIndex) as the starting index.
+  // We do this by rounding down the `SecondIndex` to the nearest multiple of
+  // VF. The minimum value and the index of the minimum value are computed for
+  // this chunk. In the second phase, we process all chunks which are multiple
+  // of VF. In the third phase, we process the last chunk which is not multiple
+  // of VF. The third phase is required because the FirstIndex is necessary to
+  // start from zero thus we take max(0, FirstIndex) as the starting index.
 
   // Overview of the algorithm to compute minindex within a chunk:
   // 1. We compare the current loaded vector against a splat of infinity.
-  // 2. Further, we set the bits until we find the first set bit in the output of the
-  // above comparison. This is realized using the `cttz` intrinsic.
-  // 3. Next, we count the number of bits set and this gives us the offset from the
-  // base. The base of the chunk is updated in each phase.
-  // Step 1 and 2 are done using brkb + cnt which is realized using the `cttz` intrinsic.
+  // 2. Further, we set the bits until we find the first set bit in the output
+  // of the above comparison. This is realized using the `cttz` intrinsic.
+  // 3. Next, we count the number of bits set and this gives us the offset from
+  // the base. The base of the chunk is updated in each phase. Step 1 and 2 are
+  // done using brkb + cnt which is realized using the `cttz` intrinsic.
 
   // The below basic blocks are used to process the first phase
   // and are for processing the chunk which is not multiple of VF.
@@ -468,7 +468,7 @@ bool LoopIdiomVectorize::transformMinIdxPattern(
       BasicBlock::Create(Ctx, "minidx.partial.1.if", F);
   BasicBlock *MinIdxPartial1ProcExit =
       BasicBlock::Create(Ctx, "minidx.partial.1.proc.exit", F);
-  
+
   // The below basic blocks are used to process the second phase
   // and are for processing the chunks which are multiple of VF.
   BasicBlock *MinIdxWhileBodyLrPh =
@@ -511,8 +511,8 @@ bool LoopIdiomVectorize::transformMinIdxPattern(
       Builder.CreateSub(ConstantInt::get(I64Ty, 0), VLen, "minidx.not");
   Value *And = Builder.CreateAnd(SecondIndex, Not, "minidx.and");
 
-  // %minidx.umax = tail call i64 @llvm.umax.i64(i64 %minidx.and, i64 %FirstIndex)
-  // %minidx.add = add i64 %SecondIndex, 1
+  // %minidx.umax = tail call i64 @llvm.umax.i64(i64 %minidx.and, i64
+  // %FirstIndex) %minidx.add = add i64 %SecondIndex, 1
   Value *Umax = Builder.CreateIntrinsic(
       Intrinsic::smax, {I64Ty}, {And, FirstIndex}, nullptr, "minidx.umax");
   Value *Add =

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https://github.com/llvm/llvm-project/pull/144987