Add a regression test for mlir-stage-15-v1

This adds one LIT test covering 1 line and 1 branch outcome that the existing suite does not reach, across 1 source file, at 48615bc5925ef4b9db8b4550b5d4322933cf4b7b.

Coverage this test adds

Source file	Newly covered lines	Newly covered branch outcomes
lib/Frontend/Raising/MaterializeFMulAddPass.cpp	178	177:9–177:25 true

lib/Frontend/Raising/MaterializeFMulAddPass.cpp

 175          }); 176  +177      if (selected.empty())    [true branch at 177:9]+178        return markAllAnalysesPreserved(); 179   180      materializeSelected(getContext(), selected, shape.getValue());

The test

The input was reduced from 6 to 1 lines while keeping every covered line and branch outcome above, and while the compiler still accepted it. The CHECK lines are the compiler's exact output on this input at 48615bc5925ef4b9db8b4550b5d4322933cf4b7b.

// RUN: loom-raise-opt --loom-materialize-fmuladd=shape=fused %s | FileCheck %s



// CHECK: module {
// CHECK-NEXT: }
// CHECK-EMPTY:

Validation

• Native compiler and FileCheck replay: passed at 48615bc5925ef4b9db8b4550b5d4322933cf4b7b.
• Property checker verdict on the reduced pair: PASS (postcondition.spct, SHA-256 32c2f1137fecabff3bcd614b253f87a8b83c567b0b3388187885ee0a1c0a5e59).
• Reduction criterion: accepted checker PASS and every original line/branch increment over the suite baseline; the original postcondition BDD decision path is unchanged; every original fast edge increment over its suite baseline.

Where this test came from

PBT mlir-stage-15-v1, run 20260911-084459, seed 25.

The property under test is anchored on documentation:

• selected output: docs/spec-compiler-part-2-scf.md lines 185–186 (output side)
• linked input 61: docs/spec-compiler-part-2-scf.md lines 1018–1021 (input side)
• linked input 101: docs/spec-compiler-part-2-scf.md lines 178–181 (input side)
• linked input 127: docs/spec-compiler-part-2-scf.md lines 1021–1022 (input side)
• linked input 165: docs/spec-compiler-part-2-scf.md lines 1029–1034 (input side)
• linked input 209: docs/spec-compiler-part-2-scf.md lines 181–185 (input side)

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Coverage is measured against the recorded baseline suite at this revision, and counts unique mapped file locations including generated code. Reduction retains every added line or branch outcome and a passing property check; it is not a claim of global minimality, nor of a defect.