[Mlir-commits] [mlir] cd2d736 - [mlir][tosa] Limit right-shift to 31 bits

[Rob Suderman]

Author: Rob Suderman
Date: 2022-01-20T14:39:57-08:00
New Revision: cd2d7369639e70df17e7977ac3a4a5b7854043fa

URL: https://github.com/llvm/llvm-project/commit/cd2d7369639e70df17e7977ac3a4a5b7854043fa
DIFF: https://github.com/llvm/llvm-project/commit/cd2d7369639e70df17e7977ac3a4a5b7854043fa.diff

LOG: [mlir][tosa] Limit right-shift to 31 bits

Right shift can occur that is a 32-bit right shift. This is undefined behavior.

Reviewed By: mehdi_amini

Differential Revision: https://reviews.llvm.org/D117732

Added: 
    

Modified: 
    mlir/lib/Dialect/Tosa/Utils/QuantUtils.cpp

Removed: 
    


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diff  --git a/mlir/lib/Dialect/Tosa/Utils/QuantUtils.cpp b/mlir/lib/Dialect/Tosa/Utils/QuantUtils.cpp
index ff82acec21e97..3fa471c37f312 100644
--- a/mlir/lib/Dialect/Tosa/Utils/QuantUtils.cpp
+++ b/mlir/lib/Dialect/Tosa/Utils/QuantUtils.cpp
@@ -46,8 +46,8 @@ static void computeMultiplierAndShiftTosaScale16(double scale,
 
   // Shifting tops out at 63 bits. Right shift to make 63 bits the max.
   if (shift > 63) {
-    // Shifting the multiplier by more than 32-bits is unnecessary.
-    multiplier = multiplier >> std::min<int32_t>(32, shift - 63);
+    // Shifting the multiplier by more than 31-bits is unnecessary.
+    multiplier = multiplier >> std::min<int32_t>(31, shift - 63);
     shift = 63;
   }
 }
@@ -82,7 +82,7 @@ static void computeMultiplierAndShiftTosaScale32(double scale,
   // Shifting tops out at 63 bits. Right shift to make 63 bits the max.
   if (shift > 63) {
     // Shifting the multiplier by more than 32-bits is unnecessary.
-    multiplier = multiplier >> std::min<int32_t>(32, shift - 63);
+    multiplier = multiplier >> std::min<int32_t>(31, shift - 63);
     shift = 63;
   }
 }